Transmissive imaging and related apparatus and methods

ABSTRACT

Apparatus and methods are described that include ultrasound imaging devices, which may operate in a transmissive ultrasound imaging modality, and which may be used to detect properties of interest of a subject such as index of refraction, density and/or speed of sound. Devices suitable for performing high intensity focused ultrasound (HIFU), as well as HIFU and ultrasound imaging, are also described.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit under 35 U.S.C. §119(e) of U.S.Provisional Patent Application Ser. No. 61/548,047, entitled “OPPOSEDARRAY IMAGING AND RELATED APPARATUS AND METHODS” filed on Oct. 17, 2011under Attorney Docket No. B1348.70000US00, which is herein incorporatedby reference in its entirety.

BACKGROUND

Imaging technologies are used for multiple purposes. One purpose is tonon-invasively diagnose patients. Another purpose is to monitor theperformance of medical procedures, such as surgical procedures. Yetanother purpose is to monitor post-treatment progress or recovery. Thus,medical imaging technology is used at various stages of medical care.

The value of a given medical imaging technology depends on variousfactors. Such factors include the quality of the images produced (interms of resolution or otherwise), the speed at which the images can beproduced, the accessibility of the technology to various types ofpatients and providers, the potential risks and side effects of thetechnology to the patient, the impact on patient comfort, and the costof the technology. The ability to produce three dimensional images isalso a consideration for some applications.

Different types of medical imaging technologies have different strengthsand weaknesses with respect to the above-listed factors. Typically, thespeed of a particular imaging system, and therefore its usefulness invarious time-constrained environments such as emergency rooms, iscompromised as the resolution is increased. For instance, magneticresonance imaging (MRI) can provide high resolution images of varioustypes of tissue, but is generally very slow, and suffers from otherdrawbacks including high cost, loud noise, and the use of potentiallyharmful magnetic field strengths. In contrast, conventional medicalultrasound imaging is implemented with less expensive equipment whichproduces images more quickly than MRI. Yet, the resolution ofconventional ultrasound imaging is typically less than that of MRI, andthe type of data collected is different.

Conventional techniques for producing three-dimensional images involveimaging multiple two-dimensional cross-sections, or “slices” of a volumeto be imaged, and then stacking the distinct images of the slicestogether. Such techniques provide a limited interpretation of athree-dimensional object. Moreover, at least some such techniquesrequire the mechanical scanning of the imaging device over the area ofinterest, which adds substantially to the time required to collect thedata for the image. Accordingly, what is needed, for example, is animaging technology that produces high resolution, volumetricthree-dimensional images in a short time.

SUMMARY OF EMBODIMENTS

Provided herein are numerous embodiments of systems, apparatus, andmethods for providing imaging and/or high intensity focused ultrasound(HIFU) and/or thermometry functionality. The provision of thisfunctionality, as described herein, may be supported by underlyingtechnology, including in relation to imaging and/or HIFU and/orthermometry element arrays, measurement geometry, front-end processingcircuitry and techniques, image reconstruction, and/or athree-dimensional (3D) interface, according to numerous non-limitingembodiments as described in detail throughout the application. Each ofthe systems, apparatus and methods described herein may include any oneor any combination of these or other underlying technological features.

In a first aspect according to some embodiments, imaging and/or HIFUand/or thermometry element arrays may facilitate the provision ofimaging and/or HIFU and/or thermometry functionality by the systems,apparatus, and methods described herein. Arrays of imaging elementsand/or arrays of HIFU elements (individually or in combination) mayutilize various types of imaging and/or HIFU elements in variouslayouts. Imaging elements may also be used for thermometry. Variousmaterials may be used to form the elements, examples of which aredescribed herein. The elements may assume suitable layouts to providedesired functionality, such as being arranged in arrays, being sparselyarranged, and/or irregularly arranged, as non-limiting examples.Additional features of suitable layouts according to some embodimentsare described in detail throughout the application.

In a second aspect according to some embodiments, measurement geometrymay facilitate the provision of imaging and/or HIFU and/or thermometryfunctionality by the systems, apparatus, and methods described herein.Elements configured as imaging elements may be separated in space insome embodiments, for example being arranged in an opposed relationshipof sources and sensors. In some embodiments, multiple (e.g., all, or atleast two, three, four, five, ten, twenty, fifty, 100, etc.) pairscorrelation, described in detail below in connection with non-limitingembodiments, is utilized and is facilitated by the separation of sourcesfrom sensors. Alternatively or additionally, the relative and/orabsolute positions of elements may be tracked in some embodiments, forexample to facilitate processing of data collected by sensors. Variousnon-limiting embodiments of position tracking are described in detailbelow.

In a third aspect according to some embodiments, front-end processingcircuitry and techniques for imaging and/or HIFU and/or thermometrysystems may facilitate the provision of imaging and/or HIFU and/orthermometry functionality by the systems, apparatus, and methodsdescribed herein. Suitable circuitry (e.g., analog and/or digital) forgenerating suitable signals to be transmitted and received by an imagingand/or HIFU and/or thermometry system are provided. In some embodiments,beamforming is utilized in the imaging and/or HIFU and/or thermometrycontext, and may be facilitated by use of suitable analog and/or digitalsignal chain circuitry. Various waveforms may be constructed for use inimaging and/or HIFU systems described herein, and they may be processedin any suitable manner. Transmission and/or receipt of transmittedsignals may be performed according to various schemes, including time—division multiple access schemes, code-divisional multiple accessschemes, and/or frequency-division multiple access schemes, amongothers. Various parameters of interest (e.g., amplitude, phase, etc.)may be extracted from received signals using various processing. Thus,accurate imaging and/or HIFU may be achieved.

In a fourth aspect according to some embodiments, image reconstructiontechnology, which may apply primarily in the context of imaging, butwhich may also facilitate HIFU operation, as described in detail below,in connection with non-limiting embodiments, may facilitate theprovision of imaging and/or HIFU and/or thermometry functionality by thesystems, apparatus, and methods described herein. In some embodiments,algebraic reconstruction techniques may be utilized. Alternatively oradditionally, in some embodiments, physical phenomena impactingcollected imaging data, such as dispersion, refraction and/ordiffraction, among others, may be accounted for in any suitable manner.Alternatively or additionally, in some embodiments, compressive sensing(sometimes termed compressed sensing) is used in image reconstruction.Images may then be used for desired analysis, such as for classificationof imaged objects (e.g., tissue classification), diagnosis (e.g., in themedical context) and/or thermometry, among others.

In a fifth aspect according to some embodiments, a three-dimensional(3D) interface may facilitate the provision of imaging and/or HIFUand/or thermometry functionality by the systems, apparatus, and methodsdescribed herein. In some embodiments, 3D images may be generated anddisplayed to a viewer. The generation and/or display of 3D images mayoccur rapidly in some embodiments, for example in real time.Alternatively or additionally, in some embodiments, a user (e.g., adoctor) may provide input via a 3D interface, for example by markingpoints of interest on a 3D image using a suitable device or handmovement. Image analysis may also be performed, in some embodiments,using any suitable techniques. In some embodiments, a user may plan alocation or path for performing a medical procedure (e.g., surgery,HIFU, etc.) by viewing and/or interacting with a 3D image in the mannersdescribed in detail below, thus allowing for 3D surgical path planningin some embodiments.

According to some embodiments of the present application, an imagingdevice (e.g., ultrasound imaging device) is provided that includesopposed arrays of radiation sources and sensors (e.g., arrays oncompletely opposite sides of a subject to be imaged). The imaging devicemay operate in a transmissive modality in which radiation (e.g., one ormore ultrasound signals) transmitted through a subject is detected andused in generating a volumetric image of the subject. The followingdescription focuses primarily on the non-limiting embodiments ofapparatus and methods that utilize ultrasound sources and sensors forimaging, characterization, and/or treatment of the subject. In at leastsome embodiments, one or more of the ultrasound sensors may receiveultrasound signals from multiple ultrasound sources arranged in at leasttwo dimensions. The ability of one or more sensors (coupled withfront-end circuitry) to distinguish (or discriminate) between two ormore of the signals received from multiple ultrasound sources, providesa large amount of data about the subject. In at least some embodiments,the collection and then the processing of such data is performedrapidly. Thus, in some embodiments, three-dimensional (3D) volumetricimages of the subject may be rapidly generated. In at least someembodiments, the volumetric images have high resolution.

According to some embodiments of the present application, opposed arraysof ultrasound sources and sensors may be static, relative to oneanother, while operating, yet still provide data sufficient forreconstructing volumetric images of a subject. The sensors of theopposed arrays may be configured to receive ultrasound signalsoriginating from multiple sources whose positions define a substantialsolid angle with respect to each sensor, such as, for example, a solidangle of at least π/10 steradians, at least π/5 steradians, at least π/4steradians, at least π/2 steradians, at least π steradians, at least 2πsteradians, between approximately π/10 and 2π steradians, betweenapproximately π/5 and π steradians, or any other suitable non-zero solidangle. For example, such a configuration is described with respect tonon-zero solid angle 420 in FIG. 4, below. The absence of anyrequirement to move the arrays during operation may facilitate rapidvolumetric imaging. In some embodiments, the opposed arrays may beindividually and/or relatively movable.

According to some embodiments of the present application, a system andmethod are provided for rapid collection of data about a volume ofinterest (e.g., a volume containing a subject). The system and methodmay employ transmissive ultrasound techniques, for example, in whichultrasound sources positioned on one side of the volume are configuredto transmit ultrasound signals through the volume to ultrasound sensorson an opposed side of the volume. The signals received by the ultrasoundsensors may be discriminated to determine from which ultrasound sourcethe signals were emitted. The received signals may be analyzed todetermine signal characteristics such as amplitude, frequency, phase,and/or other characteristics. Such characteristics may represent orotherwise be indicative of the attenuation of the signals while passingthrough the volume, a phase shift of the signals while passing throughthe volume, and/or time-of-flight (TOF) of the signals while passingthrough the volume. From such information, properties of the volumebeing imaged (or a subject therein) may be determined, such as density,index of refraction, temperature, and/or speed of sound, as non-limitingexamples.

According to some embodiments of the present application, methods andsystems for performing rapid (e.g., real time) volumetric ultrasoundimaging of a subject are provided. Data about a subject, such asdensity, index of refraction, temperature, and/or speed of sound, may becollected as described above using transmissive ultrasound techniques orany other suitable techniques. One or more volumetric images of suchproperties may be generated. In some embodiments, the system may beconfigured to produce multiple volumetric images of a subject persecond, for example up to six images or more per second. In someembodiments, collection of data and/or reconstruction of volumetricimages may be performed at a rate up to approximately six frames/secondor more (e.g., between any of one, two, three, four, five, six, seven,eight, nine, or ten frames per second on one hand, and any of fifteen,twenty, twenty-five, thirty, forty, fifty, sixty, seventy, eighty,ninety, and 100 frames per second, on the other hand, and ranges inbetween), where a frame represents a grouping (or set) of data values,for example sufficient to form a single image. In some embodiments, aframe may include a data value corresponding to each radiation source ofa system. In other embodiments, a frame may include a data value foreach radiation source of a subset of radiation sources of a system.

According to some embodiments of the present application, measurementsobtained by an ultrasound imaging device may be used to construct avolumetric image of a subject. A volumetric image may be organized inthree-dimensional sub-blocks called “voxels”—analogous to pixels in atwo-dimensional image—with each voxel associated with one or more valuesof a property (e.g., index of refraction, density, temperature, speed ofsound, etc.) of the subject at a location in three-dimensional space.

Any technique or group of techniques used to construct a volumetricimage of a subject from measurements of the subject, obtained by animaging device (e.g., an ultrasound imaging device or any other suitableimaging device), is herein referred to as an image reconstructionprocess. In one embodiment, a compressive sensing (CS) imagereconstruction process may be used to calculate a volumetric image ofthe subject from measurements obtained by an imaging device (e.g., anultrasound imaging device of any of the types described herein). A CSimage reconstruction process may calculate a volumetric image of thesubject based, at least in part, on a sparsity basis in which thevolumetric image may be sparse. It should be appreciated that sparsityof a volumetric image is not the same as, and is independent from,sparsity of elements in an array. A volumetric image may be sparse in asparsity basis regardless of whether or not elements in an imaging arrayused to obtain the volumetric image are sparse. A CS imagereconstruction process may take into account the geometry of any sourcesand sensors of the imaging device to calculate a volumetric image of thesubject from measurements obtained by the imaging device. CS imagereconstruction processes and other image reconstruction processes thatmay be used in accordance with embodiments of the present applicationare described in greater detail below.

According to an aspect of the present application, movable supports aredescribed including arrangements of ultrasound elements configured assources and sensors. The ultrasound elements may cooperatively operateto image a subject in a transmissive ultrasound modality. For example,all, substantially all, most, or at least a portion of the ultrasoundradiation (e.g., at least 95%, 90%, 80%, 75%, 70%, 60%, 50%, or 40%,etc.) detected and utilized by the sensors may be transmissiveradiation. In some embodiments, scattered radiation (e.g.,back-scattered and/or forward-scattered radiation) may also be detectedand utilized at least in part. The movable supports may be handheld, andmay take the form of paddles in some non-limiting embodiments. Portableimaging devices may be realized, allowing flexibility in terms oftreatment location and angle of imaging of a subject, for example byallowing for easy repositioning of arrangements of ultrasound elementsduring operation. The cooperative operation of the arrangements ofultrasound elements may be facilitated by detection of the orientationand/or positioning (absolute or relative) of the arrangements.

According to some embodiments of the present application, a sparsearrangement of ultrasound sources and/or sensors is provided. Theultrasound sources and/or sensors may be sparsely spaced with respect toeach other compared to an operation wavelength (e.g., a centerwavelength) of the sources and/or sensors. The sparse spacing of theultrasound sources and/or sensors may reduce the number of sourcesand/or sensors required to achieve a particular imaging resolution ofinterest. The sparse spacing of ultrasound sources and/or sensors mayallow for the arrangement to include multiple types of elements.

According to some embodiments of the present application, an irregulararrangement of ultrasound sources and/or sensors is provided. Thearrangement may be irregular in that at least some of the sources and/orsensors may not be regularly spaced with respect to neighboring sourcesand/or sensors. The irregular spacing may relax design tolerances ofultrasound arrangements and allow for flexibility in operation ofultrasound devices incorporating such arrangements, such as ultrasoundimaging devices. The irregular spacing of ultrasound sources and/orsensors may lead to fewer artifacts in images calculated frommeasurements obtained by the ultrasound sensors. The irregular spacingmay lead to fewer artifacts that ordinarily result from symmetry inregular sensor arrangements. In at least some embodiments, theultrasound elements may be randomly arranged.

According to some embodiments of the present application, an arrangementof ultrasound sources and/or sensors is provided that does not fullyenclose a subject, but which is still suitable for performing volumetricimaging of the subject without any need to move the arrangement. In atleast some such embodiments, the arrangement may be substantiallyplanar, though other configurations are also possible.

According to some embodiments of the present application, apparatus, andmethods for performing high intensity focused ultrasound (HIFU) areprovided. The apparatus may include ultrasound elements configured tooperate as HIFU elements arranged among ultrasound elements configuredto operate as ultrasound imaging elements (e.g., imaging sources and/orsensors). In at least some embodiments, an apparatus is configured tooperate as a multi-mode device (e.g., a dual-mode device) for performingHIFU and ultrasound imaging. In at least some embodiments, the apparatusmay include HIFU elements interleaved among imaging elements,interspersed among imaging elements, between imaging elements, and/orarranged in another configuration.

According to some embodiments of the present application, apparatus andmethods for performing thermometry using opposed pairs of ultrasoundsources and sensors is provided. The opposed pairs may operate incombination in a transmissive ultrasound modality. Data detected fromsuch transmissive ultrasound operation may provide an indication oftemperature. For example, data detected from transmissive ultrasoundoperation may be indicative of changes in speed of sound through asubject, which in turn may be indicative of changes in temperature ofthe subject. Speed of sound and changes in speed of sound through asubject may be obtained from time-of-flight (TOF) data collected by asource-sensor pairs, attenuation data collected by source-sensor pairs,and/or any suitable combination thereof. In some embodiments, rawwaveforms collected by ultrasound sensors operating in combination withultrasound sources in a transmissive modality may be analyzed forchanges (e.g., changes in amplitude, phase, TOF, attenuation, etc.).Such changes may be indicative of changes in temperature of a subject.Measurement of temperature and temperature changes may be used alone orin combination with other operations, such as imaging and/or HIFU.

Conventional techniques for producing three-dimensional images involveimaging multiple two-dimensional cross-sections, or “slices” of a volumeto be imaged, and then stacking the distinct images of the slicestogether. Such techniques provide a limited interpretation of athree-dimensional object because the collected data represents a limitednumber of paths through a subject, the paths being confined to a givenslice.

Thus, an aspect of the present application provides an apparatus,comprising a plurality of radiation sources comprising a first radiationsource, a second radiation source, and a third radiation source. Theapparatus further comprises a first radiation sensor and a secondradiation sensor, and processing circuitry coupled to the firstradiation sensor and the second radiation sensor and configured toreceive and discriminate between, for each of the first and secondradiation sensors, respective source signals emitted by the first,second, and third radiation sources. The first radiation source, thesecond radiation source, and the first radiation sensor may lie in afirst plane, and the second radiation source, the third radiationsource, and the second radiation sensor may lie in a second planedifferent than the first plane.

Another aspect of the present application provides an apparatuscomprising a plurality of radiation sources comprising a first radiationsource, a second radiation source, and a third radiation source. Theapparatus further comprises a first radiation sensor and a secondradiation sensor, and processing circuitry coupled to the firstradiation sensor and the second radiation sensor and configured toreceive and discriminate between, for each of the first and secondradiation sensors, respective source signals emitted by the first, thesecond, and the third radiation sources. Respective center points of thefirst radiation source, the second radiation source, the third radiationsource, and the first radiation sensor may define a first non-zero solidangle having its vertex positioned at the center point of the firstradiation sensor. The respective center points of the first radiationsource, the second radiation source, and the third radiation source,together with a center point of the second radiation sensor define asecond non-zero solid angle having its vertex positioned at the centerpoint of the second radiation sensor.

According to an aspect of the present application, an apparatus isprovided comprising a plurality of radiation sources arrangednonlinearly in a first plane or three-dimensional space and configuredto emit respective source signals through a volume to be characterized.The apparatus may comprise a plurality of radiation sensors arrangednonlinearly in a second plane or three-dimensional space and configuredto oppose the first plane or three-dimensional space, and the volume,wherein each of the plurality of radiation sensors is configured tosense the source signals emitted by each of the plurality of radiationsources after the source signals pass through the volume. The apparatusmay comprise processing circuitry coupled to the plurality of radiationsensors and configured to receive and discriminate between the sourcesignals sensed by the plurality of radiation sensors. The receivedsignals may be indicative of at least one characteristic of the volume.

According to an aspect of the present application, an apparatuscomprises a plurality of radiation sources configured to emit respectivesource radiation signals incident upon a volume to be characterized, thevolume spanning orthogonal X, Y, and Z axes. The plurality of radiationsources may occupy multiple locations in the X direction and multiplelocations in the Y direction. The apparatus may further comprise aplurality of radiation sensors separated from the plurality of radiationsources along the Z direction and configured to sense the respectivesource radiation signals emitted by the plurality of radiation sources,the plurality of radiation sensors occupying multiple locations in the Xdirection and multiple locations in the Y direction. The apparatus mayfurther comprise processing circuitry coupled to the plurality ofradiation sensors and configured to receive and discriminate between,for each of the plurality of radiation sensors, the respective sourcesignals of the plurality of radiation sources.

According to an aspect of the present application, an apparatus isprovided comprising a plurality of radiation sources configured to emitrespective source radiation signals directed to be incident upon asubject such that the respective source radiation signals pass throughthe subject along paths bounding a volume. The apparatus may comprise aradiation sensor configured to receive the respective source radiationsignals after they pass through the subject. The apparatus may furthercomprise processing circuitry coupled to the radiation sensor andconfigured to discriminate between the respective source radiationsignals.

According to an aspect of the present application, an apparatus isprovided comprising a plurality of radiation sources configured to emitrespective source radiation signals directed to be incident across asurface area of a subject. The apparatus may comprise first and secondradiation sensors each configured to sense the respective sourceradiation signals, and may also comprise processing circuitry coupled tothe first and second radiation sensors and configured to receive anddiscriminate between, for each of the first and second radiationsensors, the respective source radiation signals emitted by theplurality of radiation sources.

According to an aspect of the present application, an apparatus isprovided comprising three radiation sources arranged in amulti-dimensional, non-linear arrangement and configured to producerespective source signals. The apparatus may further comprise aplurality of radiation sensors, and processing circuitry coupled to theplurality of radiation sensors and configured to receive anddiscriminate between, for at least one radiation sensor of the pluralityof radiation sensors, the respective source signals produced by thethree radiation sources.

According to an aspect of the present application an apparatus isprovided comprising multiple arrays of ultrasound sources configured toemit respective source signals and an array of ultrasound sensorsconfigured to sense the respective source signals. The apparatus mayfurther comprise processing circuitry coupled to the array of ultrasoundsensors and configured to receive and discriminate between, for at leastone ultrasound sensor of the array of ultrasound sensors, the respectivesource signals of at least one ultrasound source from each of at leasttwo arrays of the multiple arrays of ultrasound sources.

According to an aspect of the present application, an apparatus isprovided comprising a plurality of N×M radiation sources forming atwo-dimensional or three-dimensional radiation source arrangement andconfigured to produce a first plurality of N×M respective sourcesignals, wherein N is greater than or equal to M. The apparatus mayfurther comprise a plurality of X×Y radiation sensors forming atwo-dimensional or three-dimensional radiation sensor arrangement, andprocessing circuitry coupled to the plurality of radiation sensors andconfigured to discriminate between greater than (X×Y×N) received signalsfrom the N×M respective source signals.

Conventional ultrasound imaging technologies also suffer from thedrawback that the positions of ultrasound sources and sensors havelittle freedom of motion relative to each other. Conventional ultrasounddevices therefore typically exhibit limited flexibility in movement andlimited ability to be adjusted during operation.

According to an aspect of the present application, an apparatus isprovided comprising a plurality of ultrasound elements in a fixedrelationship with respect to each other and configured as ultrasoundimaging elements, and a detector configured to dynamically detect anorientation and/or position of the plurality of ultrasound elements.

Aspects of the present application also relate to the relativepositioning of ultrasound elements of an arrangement. Conventionalultrasound devices utilize ultrasound elements that are spaced atregular intervals with respect to each other, for example along a line.Such regular spacing can create undesirable artifacts in images producedusing such devices. Also, such regular spacing represents a designconstraint, the deviation from which is not generally tolerated, asdevice performance can suffer. Furthermore, the spacing of the elementsis conventionally sufficiently close to allow for sensing of at leastsample point per wavelength of the ultrasound radiation, which placesconstraints on the spacing and number of elements required to implementan ultrasound arrangement.

According to an aspect of the present application, an apparatus isprovided, comprising a plurality of ultrasound sensors forming atwo-dimensional or three-dimensional ultrasound sensor arrangement, andprocessing circuitry coupled to the plurality of ultrasound sensors andconfigured to process signals from the plurality of ultrasound sensorsto produce ultrasound imaging data indicative of a subject imaged atleast in part by the plurality of ultrasound sensors At least someultrasound sensors of the plurality of ultrasound sensors are not spacedat regular intervals with respect to neighboring ultrasound sensors, andmay be said to create an irregular arrangement of ultrasound sensors (orelements more generally).

According to an aspect of the present application, an apparatus isprovided comprising a plurality of radiation sensors forming atwo-dimensional or three-dimensional sensor arrangement and configuredto receive radiation of wavelength λ, emitted by one or more radiationsources. The spacing between a first radiation sensor of the pluralityof radiation sensors and its nearest neighboring radiation sensor of theplurality of radiation sensors is greater than λ/2 in some embodiments,greater than λ, in some embodiments, greater than 2λ in someembodiments, and greater than 3λ, in some embodiments. Such arrangementsmay be termed sparse arrangements.

Aspects of the present application are also directed tothree-dimensional image reconstruction techniques, for example for usein generating 3D medical images. Conventional solutions toreconstruction of 3D images either require stringent geometricalconstraints of the imaging system or utilize 2D wave propagation codeswhich result in less faithful reconstructions (since use of 3D wavepropagation codes was conventionally impractical).

Accordingly, an aspect of the present application provides a methodcomprising accessing a plurality of measurements of a subject, theplurality of measurements resulting at least in part from the detectionof ultrasound radiation by an ultrasound imaging device operating in atransmissive modality, and generating, using at least one processor, atleast one volumetric image of the subject from the plurality ofmeasurements by using a compressive sensing image reconstructionprocess.

According to an aspect of the present application, a method is providedcomprising accessing at least one volumetric image of a subjectgenerated using a plurality of measurements of the subject, theplurality of measurements resulting at least in part from the detectionof ultrasound radiation by an ultrasound imaging device operating in atransmissive modality. The method further comprises applyingstereoscopic conversion to the at least one volumetric image to obtain afirst stereoscopic image and a second stereoscopic image, and displayingthree-dimensionally, via a three-dimensional display, the firststereoscopic image and the second stereoscopic image to a viewer.

According to an aspect of the present application, a method is providedcomprising accessing at least one volumetric image of a subjectcalculated using a plurality of measurements of the subject, theplurality of measurements resulting at least in part from the detectionof radiation by an imaging device. The method further comprisesidentifying a point of view within the subject, wherein identifying thepoint of view comprises identifying a location within the subject, anddisplaying the at least one volumetric image to a viewer from theidentified point of view.

According to an aspect of the present application, a method is providedcomprising accessing a plurality of measurements of a subject, theplurality of measurements resulting at least in part from the detectionof ultrasound radiation by an ultrasound imaging device, the ultrasoundimaging device comprising a plurality of ultrasound sources including afirst ultrasound source and a plurality of ultrasound sensors includinga first ultrasound sensor, and calculating, using at least oneprocessor, a first image of the subject from the plurality ofmeasurements by using first path length information for a path betweenthe first ultrasound source and the first ultrasound sensor. The methodmay further comprise calculating, using the at least one processor,second path length information at least in part by computing refractivepaths using the first image. The method may further comprisecalculating, using the at least one processor, a second image of thesubject from the plurality of measurements by using the second pathlength information.

Aspects of the present application relate to application of highintensity focused ultrasound (HIFU) to a subject. HIFU may be used forvarious purposes, such as cauterization or tissue ablation, amongothers. It may be desirable to view the location at which HIFU isapplied, for example to assess the progress or effectiveness of theHIFU. HIFU probes and imaging technologies were conventionally separate.

According to an aspect of the present application, an apparatus isprovided comprising a support, a first plurality of ultrasound elementsconfigured as ultrasound imaging elements, and a second plurality ofultrasound elements configured as high intensity focused ultrasound(HIFU) elements. The first plurality and second plurality of ultrasoundelements may be physically coupled to the first support, and at leastsome elements of the first plurality of ultrasound elements are arrangedamong at least some elements of the second plurality of ultrasoundelements.

According to an aspect of the present application a system is providedcomprising a first support, a second support, a first plurality ofultrasound elements configured as high intensity focused ultrasound(HIFU) elements and physically coupled to the first support andconfigured as a first source of HIFU, and a second plurality ofultrasound elements configured as ultrasound imaging elements andcoupled to the first support and distinct from the first plurality ofultrasound elements. The apparatus may further comprise a thirdplurality of ultrasound elements configured as HIFU elements andphysically coupled to the second support and configured as a secondsource of HIFU, and a fourth plurality of ultrasound elements configuredas ultrasound imaging elements and coupled to the second support anddistinct from the third plurality of ultrasound elements. The secondplurality of ultrasound elements and the fourth plurality of ultrasoundelements are configured to operate in combination in a transmissiveultrasound imaging modality.

According to an aspect of the present application, an apparatus isprovided comprising a substrate, a first plurality of ultrasoundelements configured as ultrasound imaging elements coupled to thesubstrate, and a second plurality of ultrasound elements configured ashigh intensity focused ultrasound (HIFU) elements coupled to thesubstrate.

An aspect of the present application provides a method comprisingdisplaying a volumetric image of a subject to a user three dimensionallyvia a three-dimensional display, obtaining user input identifying atleast one target point in the volumetric image corresponding to at leastone location in the subject, and applying high intensity focusedultrasound (HIFU) energy to the at least one location in the subject.

Conventional HIFU also suffered from the drawback of insufficientcontrol over the location which HIFU was applied, particularly when apatient moved. Misapplication of HIFU to a patient can be dangerous inaddition to being inefficient.

According to an aspect of the present application, a method is providedcomprising applying high intensity focused ultrasound (HIFU) energy to asubject, identifying, based at least in part on an image of the subject,a first target point in the subject to which the HIFU energy wasapplied, and automatically determining whether to continue applying theHIFU energy to the first target point at least in part by comparing thefirst target point to a planned target point. The method may furthercomprise continuing to apply the HIFU energy to the first target pointbased at least in part on the comparison.

According to such an aspect, accurate detection and tracking of thelocation at which HIFU is applied relative to a desired HIFU locationmay be provided. The results of such detection and tracking may be usedto control to which locations HIFU is applied. Thus, the accuracy of theHIFU application may be improved, and effectiveness and safety of theHIFU process may be increased.

Aspects of the present application relate to processing of signalsreceived by large numbers of receiving elements, for instance in thecontext of an ultrasound imaging system. Conventional signal processingtechniques of large amounts of data can be time-consuming, so that suchtechniques may substantially limit the ability to rapidly create 3Dimages (e.g., 3D ultrasound images) based on the received signals.

According to an aspect of the present application, an apparatus isprovided comprising a first ultrasound element configured as anultrasound source, and transmit circuitry coupled to the ultrasoundsource and configured to provide to the ultrasound source a transmissionsignal to be emitted by the ultrasound source. The apparatus may furthercomprise a second ultrasound element configured as an ultrasound sensorand processing circuitry coupled to the ultrasound sensor and configuredto process a signal emitted by the ultrasound source and received by theultrasound sensor. The processing circuitry may be configured to combinethe signal received by the ultrasound sensor with a reference signal toproduce a combined signal.

BRIEF DESCRIPTION OF DRAWINGS

Various aspects and embodiments of the application will be describedwith reference to the following figures. It should be appreciated thatthe figures are not necessarily drawn to scale. Items appearing inmultiple figures are indicated by the same reference number in all thefigures in which they appear.

FIG. 1A illustrates opposed arrays of radiation (e.g., ultrasound)sources and sensors, according to a non-limiting embodiment.

FIG. 1B illustrates a detailed view of a portion of the arrays of FIG.1A positioned relative to a subject of interest, according to anon-limiting embodiment.

FIG. 2 illustrates a system including radiation (e.g., ultrasound)sources and sensors and front-end circuitry, according to a non-limitingembodiment.

FIG. 3 illustrates a flowchart of the operation of the system of FIG. 2,according to a non-limiting embodiment.

FIGS. 4, 5, 6A and 6B illustrate more detailed examples of systems ofthe type illustrated in FIG. 2, according to various non-limitingembodiments.

FIGS. 7A-7C illustrate examples of signal transmitters as may beimplemented in a system in accordance with one or more embodiments ofthe present application.

FIGS. 8A and 8B illustrate examples of waveforms which may betransmitted in an imaging mode, according to a non-limiting embodiment.

FIG. 8C demonstrates an example of a waveform derived from a binarysequence by using a box-car interpolation waveform.

FIG. 9 illustrates a block diagram of a signal receiver as may beimplemented in a system in accordance with one or more embodiments ofthe present application.

FIG. 10 illustrates a more detailed example of the signal receiver ofFIG. 9, according to a non-limiting embodiment.

FIGS. 11A-11D illustrate alternative implementations of the signalreceiver of FIG. 9, according to various non-limiting embodiments.

FIG. 12 is a flowchart of a method of implementing code divisionmultiple access (CDMA) processing, according to a non-limitingembodiment.

FIG. 13 is a flowchart of an alternative to the methodology of FIG. 12,adding further processing, according to a non-limiting embodiment.

FIG. 14 illustrates a non-limiting example of an implementation of aportion of the methods of FIGS. 12 and 13.

FIG. 15 illustrates in block diagram form a signal receiver suitable forperforming CDMA processing, according to a non-limiting embodiment.

FIG. 16 illustrates a system configuration for performing time divisionmultiple access (TDMA) processing according to an embodiment of thepresent application.

FIGS. 17A and 17B are flowcharts a methods of implementing TDMAprocessing, according to non-limiting embodiments.

FIGS. 18A-18D illustrate irregular arrangements of radiation (e.g.,ultrasound) elements, according to non-limiting embodiments.

FIG. 19 illustrates a random arrangement of radiation elements,according to a non-limiting embodiment.

FIG. 20 illustrates a sparse arrangement of radiation elements,according to a non-limiting embodiment.

FIG. 21 illustrates a three-dimensional arrangement of radiationelements according to a non-limiting embodiment.

FIGS. 22A-22C illustrate imaging systems of sources and sensors,according to a non-limiting embodiment.

FIG. 23 illustrates two arrangements of radiation elements separated bya plane, according to a non-limiting embodiment.

FIG. 24 illustrates two arrangements of radiation elements separated inspace, according to a non-limiting embodiment.

FIG. 25 illustrates a plurality of movable supports includingarrangements of radiation elements, according to a non-limitingembodiment.

FIG. 26 illustrates an alternative to that of FIG. 25, in which themovable supports are coupled together by a rigid connector, according toa non-limiting embodiment.

FIG. 27 illustrates an expansion on the system of FIG. 25 in which themovable supports may communicate with each other and/or with a remotedevice to determine orientation and/or position information, accordingto a non-limiting embodiment.

FIG. 28 illustrates an apparatus utilizing flexible supports on whicharrangements of ultrasound elements may be disposed, according to anon-limiting embodiment.

FIG. 29 illustrates a flowchart of a process for generating one or morevolumetric images of a subject, according to a non-limiting embodiment.

FIG. 30 illustrates a line segment, from one ultrasound element toanother ultrasound element, which intersects a voxel in a volume to beimaged, according to a non-limiting embodiment.

FIG. 31 illustrates medical images at various levels of compression inthe discrete cosine transform domain.

FIG. 32 illustrates an imaging system, which may be used to image apatient, according to a non-limiting embodiment.

FIGS. 33A and 33B provide alternate views of an apparatus comprising anarrangement of ultrasound elements and an impedance matching component,according to a non-limiting embodiment.

FIGS. 34A, 34B, and 35A-35I illustrate examples of apparatus includingarrangements of ultrasound elements configured to perform HIFU andradiation (e.g., ultrasound) elements configured to perform imaging(e.g., ultrasound imaging), according to two non-limiting embodiments.

FIGS. 36A, 36B, 37 and 38 illustrate alternative configurations ofradiation elements that may be used in an apparatus to perform highintensity focused ultrasound (HIFU) and ultrasound imaging, according tonon-limiting embodiments.

FIG. 39 illustrates a system including two movable supports includingultrasound elements configured as imaging elements and ultrasoundelements configured as HIFU elements, according to a non-limitingembodiment.

FIG. 40 illustrates a three-dimensional (3D) temperature profileaccording to a non-limiting embodiment.

FIG. 41 is a flowchart of a process for presenting one or morevolumetric images to a viewer using a three-dimensional (3D) display,according to some non-limiting embodiments.

FIG. 42 illustrates an example of displaying stereoscopic images,obtained from a volumetric image, by using a 3D display, according tosome non-limiting embodiments.

FIG. 43 illustrates a system in which a user may view and manipulate a3D image, according to a non-limiting embodiment.

FIG. 44 is a flowchart of a process for displaying images from multiplepoints of view within the subject being imaged, according to somenon-limiting embodiments.

FIG. 45 is a flowchart of a process for identifying a path at leastpartially intersecting a subject being imaged and applying HIFU alongthe identified path, according to some non-limiting embodiments.

FIG. 46 is a flowchart of a process for correcting how HIFU is appliedto a subject based on one or more volumetric images of the subject,according to some non-limiting embodiments.

FIG. 47 illustrates an embodiment in which an arrangement of radiationelements (e.g., ultrasound elements) does not occupy a substantial solidangle having its vertex located at the position of a subject.

DETAILED DESCRIPTION OF EMBODIMENTS

Various embodiments described herein relate to imaging technology, bothmedical as well as that used for non-medical purposes. Imagingtechnologies generally require detection of radiation, which may takevarious forms. Various embodiments described herein apply irrespectiveof the type of radiation utilized. For purposes of illustration, thefollowing description focuses on ultrasound radiation, and thereforemany of the systems and methods disclosed are described as utilizingultrasound radiation and ultrasound components. However, unless clearlyindicated to the contrary, any reference to ultrasound is a non-limitingexample and should be interpreted to also contemplate other types ofradiation more generally. As an example, reference to an “ultrasoundelement” should be understood to be a non-limiting example, with themore general embodiment of “radiation element” also being contemplatedherein.

Non-limiting examples of radiation to which embodiments of the presentapplication may apply, in addition to ultrasound, includeelectromagnetic radiation as well as acoustic radiation other thanultrasound radiation (e.g., subsonic radiation). Examples include anytransfer of photons, and electromagnetic radiation (gamma-rays throughx-rays, ultraviolet, visible, infrared (IR), THz, and microwave, asnon-limiting examples). Non-limiting examples of imaging types to whichembodiments of the present application may apply (in addition toultrasound, described in detail below) include electrical impedancetomography, proton radiography, positron emission tomography (PET),Single-Photon Emission computed tomography (SPECT), and fluorescenceimaging/multi-photon imaging.

As used herein, unless indicated otherwise by the context, the term“approximately” is generally understood to mean, for example, within15%, within 10%, or within 5%, although one of skill would appreciatethere is latitude in such numbers depending on the context. As usedherein, unless indicated otherwise by the context, the term“substantially” is understood to mean, for example, within 5%, within3%, within 2%, or exactly, although one of skill would appreciate thereis latitude in such numbers depending on the context.

As used herein, the phrase “three-dimensional imaging” (and words ofsimilar import) encompasses volumetric imaging as well as slice-basedimaging (i.e., the stacking of multiple two-dimensional images to form athree-dimensional image). Volumetric imaging, to be distinguished fromslice-based imaging, may be described, in some embodiments, as imagingin which sensors receive signals transmitted from sources arranged in atleast two dimensions, imaging in which sensors receive signalstransmitted by sources defining a non-zero solid angle, non-planarimaging, non-tomographic imaging, or imaging in which a sensor receivessignals transmitted by sources arranged in a same plane as the sensor inaddition to signals transmitted by sources not arranged in the sameplane as the sensor. Examples are described further below. In someembodiments, two or more of the received signals may be distinguished(or discriminated) from each other, such that discrete measurements maybe provided corresponding to particular source from which a sensorreceives a signal. As will be described further below, discriminationbetween signals in various embodiments may be accomplished using codedivision multiple access (CDMA) modes, time division multiple access(TDMA) modes, frequency division multiplexing (FDM) modes, as well ascombinations of any of two or more of these modes of operation.

It should be appreciated that various types of subjects may be analyzedand imaged according to the aspects described herein. The subjects maybe human (e.g., medical patients), though not all embodiments arelimited in this respect. For example, one or more aspects describedherein may be used to analyze and image animals, bags, packages,structures, or other subjects of interest. As another example, one ormore aspects described herein may be used to analyze and image smallanimals Thus, the aspects described herein are not limited to the typeof subject being analyzed and imaged.

The aspects and embodiments described above, as well as additionalaspects and embodiments, are described further below. These aspectsand/or embodiments may be used individually, all together, or in anycombination of two or more, as the application is not limited in thisrespect.

According to some embodiments of the present application, an imagingdevice (e.g., ultrasound imaging device) having opposed arrays ofultrasound sources and sensors is provided. FIG. 1A illustrates anon-limiting example. In some embodiments, the apparatus 100 includes afirst array 102 a of ultrasound elements 104 and a second array 102 b ofultrasound elements 104. In the non-limiting example shown, each of thefirst and second arrays 102 a-102 b includes sixteen ultrasound elements104. However, other numbers of elements may be implemented, includingmore or fewer elements. For example, one or both of the arrays 102 a and102 b may have approximately 20 elements per side (e.g., a 20×20 array),approximately 32 elements per side (e.g., a 32×32 array), approximately100 ultrasound elements per side (e.g., a 100×100 array), approximately200 ultrasound elements per side (e.g., a 200×200 array), approximately500 ultrasound elements per side, such as a 512×512 array, approximatelyone thousand ultrasound elements per side, such as a 1024×1024 array,any intermediate number of ultrasound elements between ten and 1024, orany other suitable number of elements.

Moreover, it should be appreciated that the arrays 102 a and 102 b neednot have sides of equal numbers of ultrasound elements. For example, thearray 102 a and/or 102 b may be an N×M array, where N differs from M.Also, the array 102 a need not be the same size or configuration asarray 102 b. Further alternatives will be described further below.

The arrays may occupy any suitable size. According to a non-limitingembodiment, array 102 a may be approximately 1 mm×1 mm, approximately 1cm×1 cm, less than approximately 15 cm×15 cm, less than approximately100 cm×100 cm, or have any other suitable size. The size may bedetermined, to at least some extent, by subjects of interest to beinvestigated using the arrays. For example, if the apparatus 100 is tobe used to examine a human breast, the arrays 102 a and 102 b may besized accordingly to provide suitable examination. Also, the spacingbetween the arrays 102 a and 102 b may be any suitable spacing. Forexample, the arrays 102 a and 102 b may be separated (in the z-directionin FIG. 1A) by a millimeter, by a few millimeters, up to a few inches,up to a foot, up to several feet, or more, as non-limiting examples.According to a non-limiting embodiment, each of arrays 102 a and 102 bmay be approximately 1 mm×1 mm arrays, and may be separated in thez-direction by approximately 1 mm, such that the volume defined betweenthe arrays is approximately 1 cubic mm.

The ultrasound elements of the array 102 a and/or 102 b may beconfigured to operate at any suitable frequencies, which in someembodiments may depend on the size(s) of the arrays. For example, theelements of one or both of the arrays may be configured to operate at afrequency in the range of 100 KHz-10 MHz (e.g., 250 KHz, 500 KHz, 1 MHz,2.5 MHz, 5 MHz, etc.) to image a volume of approximately 10 cubic cm. Asanother example, the elements of one or both of the arrays may beconfigured to operate at approximately 40 MHz to image a volume ofapproximately 1 cubic mm. In some embodiments, the elements of one orboth of the arrays may be configured to operate at one or morefrequencies between approximately 5 MHz and approximately 50 MHz. Otherfrequencies of operation are also possible.

Furthermore, not all elements of an array need operate at the samefrequencies. For example, one or more elements of arrays 102 a may beconfigured to operate at a first frequency while one or more differentelements of the array 102 a may be configured to operate at a secondfrequency. The first and second frequencies may take any suitable valuesand may have any suitable relative values.

The arrays 102 a and 102 b of the apparatus 100 are opposed arrays inthat the two arrays are configured in an opposing relationship withrespect to each other. In the non-limiting example of FIG. 1A, the twoopposed arrays have an equal number of elements as each other and may bedescribed as having corresponding pairs of elements (i.e., each element104 of the array 102 a may be described as having a correspondingelement 104 of the array 102 b), but not all embodiments of opposedarrays according to the present application require the arrays to haveequal numbers of ultrasound elements.

Furthermore, it should be appreciated that the relative orientations ofthe arrays 102 a and 102 b shown in FIG. 1A may be varied. FIG. 1A showsan embodiment in which the arrays 102 a and 102 b may be substantiallyparallel to each other. However, alternatives are possible. For example,the array 102 a may be oriented at any suitable angle with respect toarray 102 b, such as between 0 degrees (parallel) and 90 degrees.

As illustrated in FIG. 1A, the ultrasound elements of each of the arrays102 a and 102 b may be arranged in two dimensions. For example, thearray 102 a includes ultrasound elements 104 arranged in both the x andy directions. Similarly, the array 102 b includes ultrasound elements104 arranged in both the x and y directions. The arrays 102 a and 102 bdefine therebetween a volume having a third dimension, i.e., in thez-direction in the non-limiting example shown, in addition to the x andy dimensions. As will be described further below, the arrays 102 a and102 b may be used to analyze a subject located within the volume. Asshown in FIG. 1A, the arrangement of elements occupies multiple xpositions and multiple y positions (e.g., a first element hascoordinates x₀, y₀, z₀, a second element has coordinates x₁, y₀, z₀, athird element has coordinates x₂, y₀, z₀, a fourth element hascoordinates x₃, y₀, z₀, a fifth element has coordinates x₀, y₁, z₀, asixth element has coordinates x₁, y₁, z₀, and so on). In thenon-limiting embodiment of FIG. 1A, the elements of each array have thesame z-coordinate as each other, namely z₀ for the elements of array 102b and z₁ for the elements of array 102 a. However, in some embodiments,including examples described below, the elements of an array (e.g., ofarray 102 a) may have different z-coordinates.

As should be appreciated from FIG. 1A, an arrangement of elements in twodimensions (which may also be referred to herein as a “two-dimensionalarrangement,” or a “multi-dimensional arrangement” (for arrangements intwo or more dimensions), or a “two-dimensional layout” or by othersimilar phraseology) as used herein differs from a one-dimensionalarrangement of two-dimensional elements. More generally, thedimensionality of an arrangement as used herein is independent of thedimensionality of the elements included in the arrangement. Thedimensionality of an arrangement as used herein relates to thedimensions spanned by the relative positioning of the elements of thearrangement, not to the dimensions of the individual elementsthemselves. As but a single example, three elements arranged in astraight line form a one-dimensional arrangement, irrespective of thedimensionality of the three elements themselves. By contrast, threeelements forming vertices of a triangle constitute a two-dimensionalarrangement. Numerous examples of multi-dimensional arrangements aredescribed and illustrated throughout the present application.

Also, as will be described further below, the two-dimensionalarrangements of the arrays 102 a and 102 b are non-limiting. In someembodiments, one or both of arrays 102 a and 102 b may employarrangements in three dimensions. Thus, FIG. 1A represents anon-limiting example only.

According to one embodiment, the ultrasound elements 104 of the array102 a may be configured as ultrasound sources while the ultrasoundelements 104 of the array 102 b may be configured as ultrasound sensors,or vice versa. For ease of explanation, the following descriptionassumes that the ultrasound elements 104 of array 102 a are configuredas ultrasound sources while the ultrasound elements of the array 102 bare configured as ultrasound sensors. However, as described, not allembodiments are limited in this respect. For example, in someembodiments, one or both of arrays 102 a and 102 b may include bothsources and sensors 104. Furthermore, as will be described below, one ormore of the ultrasound elements 104 may be configured to operate as bothsources and sensors, for example in a time-varying manner.

In some embodiments, ultrasound elements 104 configured as ultrasoundsources may be of the same type as ultrasound elements 104 configured asultrasound sensors. The difference in configuration may relate to themanner in which the ultrasound elements are electrically configured(e.g., the circuitry to which the ultrasound elements are electricallycoupled). Alternatively, in some embodiments, ultrasound elements 104configured as ultrasound sources may be of a different type thanultrasound elements 104 configured as ultrasound sensors.

The opposed arrays 102 a-102 b of apparatus 100 may be configured tooperate in a transmissive ultrasound mode. Whereas conventionalultrasound imaging devices operate primarily by detection of ultrasoundsignals reflected back toward the source of the signals, the apparatus100 may be operated such that the ultrasound elements 104 of array 102 aare configured to transmit ultrasound signals toward the ultrasoundelements 104 of array 102 b, which receive (e.g., sense or detect) thetransmitted ultrasound signals sourced (e.g., radiated or emitted) bythe ultrasound elements 104 of the array 102 a. In this manner,detection of ultrasound signals transmitted through a subject ofinterest (not illustrated in FIG. 1A) may be performed. For instance,assuming that the subject is a patient, the array 102 a may be disposedon the patient's front side while the array 102 b is disposed on thepatient's back side. The ultrasound elements 104 of array 102 a maytransmit ultrasound signals which pass through the patient to theultrasound elements 104 of the array 102 b. Alternatively oradditionally, in some embodiments scattered (e.g., back-scattered and/orforward-scattered) ultrasound radiation may be utilized (e.g., when oneor both of arrays 102 a and/or 102(b) include both ultrasound sourcesand sensors).

FIG. 1A illustrates the general paths of ultrasound rays between theultrasound elements 104 of array 102 a and ultrasound elements 104 ofarray 102 b. As illustrated, a distinct ray may be drawn between eachpair of ultrasound elements 104 that includes an ultrasound element fromthe first array 102 a and an ultrasound element from the second array102 b.

Thus, it should be appreciated that one or more (e.g., all of)ultrasound elements 104 of a first of the arrays may each communicatewith one or multiple ultrasound elements 104 (e.g., all of) of theopposing array. Moreover, one or more ultrasound elements of one of thearrays may each communicate with one or multiple ultrasound elements ofthe opposing array arranged in at least two dimensions. A non-limitingexample is described with respect to ultrasound elements 108, 110, 112,114, and 116. To facilitate understanding, these ultrasound elements(108-116) are assigned individual reference numbers even though they areall ultrasound elements 104.

As illustrated, the ultrasound element 108 may be an element of array102 b, and may, for purposes of explanation, be configured as a sensorfor receiving ultrasound signals. As shown, the ultrasound element 108may be configured to receive ultrasound signals from each of ultrasoundelements 110, 112, 114, and 116 (e.g., among others) of array 102 a, asillustrated by the corresponding rays. The ultrasound elements 110, 112,114, and 116 are arranged in two dimensions (i.e., they are arranged inthe x and y directions of FIG. 1A with respect to each other). Thus, theultrasound element 108 is configured to receive ultrasound signalstransmitted from a plurality of ultrasound elements 110, 112, 114, and116 of the array 102 a arranged in two dimensions. Moreover, the signalsreceived by the ultrasound element 108 from the plurality of ultrasoundelements 110, 112, 114 and 116 may be discriminated from each other,thus providing multiple distinct measurements corresponding to theultrasound element 108. As described further below (e.g., in connectionwith FIGS. 4, 5, 6A, and 6B, among others), suitable processingcircuitry may be coupled to the ultrasound element 108 (among others ofthe array 102 b) to facilitate discrimination between the signalsreceived from a plurality of ultrasound elements of array 102 a.

FIG. 1B provides a more detailed view of the operation just describedrelating to ultrasound elements 108-116. Also shown is a subject 118,positioned relative to the ultrasound elements 108-116 such that signalsemitted from the ultrasound elements 110-116 pass through the subject118 to be sensed (or received) by the ultrasound element 108. Thedetailed view of FIG. 1B reinforces the previous description of FIG. 1Aas providing operation in which an ultrasound element (e.g., ultrasoundelement 108) may receive signals from ultrasound sources (e.g.,ultrasound elements 110-116) arranged in two dimensions.

FIG. 1B also makes clear that in some embodiments an ultrasound elementmay be configured to receive signals emitted by ultrasound sources(e.g., ultrasound elements 110-116) lying in different planes (e.g.,imaging planes) with respect to the ultrasound element receiving thesignals. Namely, FIG. 1B illustrates that ultrasound elements 108, 114and 116 lie in a first plane P₁. Ultrasound elements 108, 110, and 112lie in a second plane P₂. The planes may intersect the respective centerpoints of the ultrasound elements, as a non-limiting example. Forinstance, plane P₁ may intersect the respective center points c₁₀₈,c₁₁₄, and c₁₁₆ of ultrasound elements 108, 114 and 116. The plane P₂ mayintersect the respective center points c₁₀₈, c₁₁₀, and c₁₁₂ ofultrasound elements 108, 110 and 112.

Thus, embodiments of the present application provide an apparatus inwhich one or more ultrasound sensors are configured to sense or receivesignals emitted by multiple ultrasound sources defining multipledifferent planes with respect to the sensor. In this manner, non-slicebased imaging (which may also be referred to herein as “out-of-plane”imaging) may be provided according to some embodiments. Referring againto FIG. 1A and considering the rays 106, it can be seen that one or moreultrasound elements (e.g., ultrasound element 108) may each beconfigured to receive signals from ultrasound sources lying in multiple,and in some cases numerous, planes with respect to the ultrasoundelement(s) receiving the signals. The distances (or angles) between suchplanes will depend on the spacing between the ultrasound elementsemitting the signals. For instance, considering FIGS. 1A and 1B incombination, the angle between P₁ and P₂ will depend to some extent onthe distance in the x-direction between x-coordinates x₂ and x₃ (in FIG.1A). However, it is to be appreciated that the planes P₁ and P₂ aredistinct.

FIG. 1B also makes clear that embodiments of the present applicationprovide an apparatus in which an ultrasound element configured as asensor receives signals emitted from multiple ultrasound elementsconfigured as ultrasound sources which, together with the ultrasoundelement configured as a sensor, define a non-zero solid angle. Forexample, a solid angle having its vertex located at the center pointc₁₀₈ of ultrasound element 108 may be defined by ultrasound elements108, 110, 112, 114 and 116. Considering again FIG. 1A, it is to beappreciated that multiple solid angles may be defined by consideringvarious combinations of the ultrasound elements 104 of arrays 102 a and102 b. A further example is described with respect to solid angles 420and 422 of FIG. 4, described below.

FIGS. 1A and 1B also illustrate that embodiments of the presentapplication provide an apparatus in which a plurality of radiationsources (e.g., ultrasound elements 104 of array 102 a) are configured toemit respective sources signals incident upon a volume to becharacterized spanning orthogonal x, y, and z axes (e.g., the volumebetween arrays 102 a and 102 b). A plurality of radiation sensors (e.g.,ultrasound elements 104 of array 102 b) may be separated from theplurality of radiation sources in the z-direction. Both the radiationsources and the radiation sensors may occupy multiple locations in the xand y-directions. Such an apparatus may be operated suitably so that theradiation sensors receive respective source signals emitted by theradiation sources and that such signals are capable of beingdiscriminated from one another (e.g., by suitable processing). In somesuch embodiments, receipt of and discrimination between the receivedsignals may be performed for each of two or more (but not necessarilyall) of the radiation sensors.

FIG. 1B also illustrates that embodiments of the present applicationprovide an apparatus in which an ultrasound element (e.g., ultrasoundelement 108) receives respective source signals emitted from ultrasoundsources positioned such that the respective emitted signals pass througha subject along paths bounding a volume. For example, FIG. 1Billustrates that respective paths between ultrasound elements 110-116and ultrasound element 108 collectively bound a volume V₁ of the subject118. In this manner, receipt of the respect source signals anddiscrimination between the received signals (e.g., using suitableprocessing circuitry) may provide information about the volume V₁,rather than simply a slice (of substantially zero thickness) of thesubject 118, and therefore may facilitate 3D imaging of the typesdescribed herein. The extent of the volume V₁ may depend on the numberand relative positioning of the ultrasound elements from which theultrasound element 108 receives respective signals. Referring to FIG.1A, it should be appreciated that a substantial volume (e.g.,significantly larger than a slice of substantially zero thickness) maybe bounded by the paths of respective signals received by any one ormore ultrasound elements configured as sensors.

FIG. 1B also illustrates that embodiments of the present applicationprovide an apparatus in which an ultrasound element (e.g., ultrasoundelement 108) receives respective source signals emitted from ultrasoundsources positioned such that the respective emitted signals are incidentacross a surface area of a subject. As shown, signals emitted byultrasound elements 110-116 may be incident across a surface area SA ofthe subject 118. The extent of the surface area may depend on the numberand relative positioning of the ultrasound elements which emitrespective source signals received by the ultrasound element 108.Referring to FIG. 1A and the illustrated rays 106, it should beappreciated that a substantial surface area (e.g., significantly largerthan would be impacted in a slice-based imaging approach) of a subjectmay be impacted by the paths of respective signals received by any oneor more ultrasound elements configured as sensors. In some embodiments,the surface area is between approximately 1 cm² and approximately 100cm². In some embodiments, the surface area may be between approximately50 cm² and approximately 100 cm², or between approximately 100 cm² and500 cm². In some embodiments, the surface area may be up to one squaremeter or more. Discrimination between respective signals (e.g., usingsuitable processing circuitry) incident across a surface area asdescribed may provide data useful for 3D imaging and/or 3D thermometryof the types described herein.

FIG. 1B also illustrates that embodiments of the present applicationprovide an apparatus in which an ultrasound element receives respectivesource radiation signals emitted by three non-linearly arrangedultrasound elements configured as sources. The sources may be arrangedin multiple dimensions. For example, ultrasound element 108 isconfigured to receive respective source signals emitted by ultrasoundelements 110, 112, and 114, which represent three non-linearly arrangedultrasound elements. Discrimination between the respective receivedsignals may be performed using suitable processing circuitry (examplesof which are described below), according to non-limiting embodiments. Itshould be appreciated by reference to FIG. 1A that multiple ultrasoundelements configured as sensors (e.g., in addition to ultrasound element108) may similarly be configured to receive respective source signalsemitted by multiple non-linearly arranged ultrasound elements configuredas sources. However, not all ultrasound elements of the array 102 bconfigured as ultrasound sensors need operate in this manner.

FIGS. 1A and 1B also illustrate that embodiments of the presentapplication provide an apparatus including a plurality of radiationsources (e.g., ultrasound elements 104 of array 102 a) arrangednonlinearly in a first plane or three-dimensional space and configuredto emit respective source signals through a volume to be characterized(e.g., imaged). A plurality of radiation sensors (e.g., ultrasoundelements 104 of array 102 b) may be arranged nonlinearly in a secondplane or three-dimensional space and configured to oppose the firstplane or three-dimensional space, and the volume. One or more (e.g.,all) of the plurality of radiation sensors may be configured to sensethe source signals emitted by one or more (e.g., all) of the pluralityof radiation sources after the source signals pass through the volume(e.g., after passing through a subject, such as subject 118). In someembodiments, processing circuitry (non-limiting examples of which aredescribed below) coupled to the plurality of radiation sensors may alsobe provided and configured to receive and discriminate between thesource signals sensed by the plurality of radiation sensors. Thereceived signals may be indicative of at least one characteristic of thevolume, such as density or refractive index, as non-limiting examples.The plurality of radiation sources and radiation sensors may be arrangedin any combination of planes and three-dimensional spaces. For example,the radiation sources may be arranged in a first plane and the radiationsensors arranged in a second plane. The radiation sources may bearranged in a plane and the radiation sensors arranged in athree-dimensional space, or vice versa. The radiation sources and theradiation sensors may be arranged in respective three-dimensionalspaces.

Considering FIG. 1A again, it is to be appreciated that in someembodiments, each ultrasound sensor may be configured to receivedistinct ultrasound signals from each ultrasound source as illustratedby the rays 106, and discrimination between such signals may be provided(e.g., using suitable processing circuitry or otherwise, non-limitingexamples of which are described in further detail below in connectionwith FIGS. 4, 5, 6A, and 6B, among others). Such operation may bereferred to as “all pairs correlation.” For example, for purposes ofillustration, the ultrasound elements 104 of array 102 b may beconfigured as ultrasound sensors while the ultrasound elements 104 ofarray 102 a may be configured as ultrasound sources, according to anon-limiting embodiment.

It should be appreciated, however, that not all embodiments are limitedto having all ultrasound elements configured as sensors receive signalsfrom all ultrasound elements configured as sources. Rather, the number(or percentage) of ultrasound sources from which ultrasound sensors mayreceive and discriminate signals may depend, for example, on the size ofthe ultrasound source arrangement, the number of ultrasound sources inthe ultrasound source arrangement, and/or the layout of the ultrasoundsource arrangement. Data sufficient for volumetric imaging (or other 3Ddata collection) may be obtained from a smaller percentage of availablesources if the arrangement of available sources has a large number,whereas receipt and discrimination between signals from a greaterpercentage of available ultrasound sources of an arrangement may bepreferred for ultrasound source arrangements having a smaller number ofultrasound sources.

For example, according to an embodiment, an ultrasound sensor of theapparatus 100 may be configured to receive, and an apparatus or systemcomprising apparatus 100 may be configured to discriminate between,distinct signals from at least 0.2% of the ultrasound sources of anopposed arrangement or array, from at least 0.5% of the ultrasoundsources of an opposed arrangement or array, at least 1% of theultrasound sources of an opposed arrangement or array, from at least 10%of the ultrasound sources of the opposed arrangement or array, from atleast 25% of the ultrasound sources of the opposed arrangement or array,from at least 40% of the ultrasound sources of the opposed arrangementor array, from at least 50% of the ultrasound sources of an opposedarrangement or array, from at least 60% of the ultrasound sources of theopposed arrangement or array, from at least 75% of the ultrasoundsources of the opposed arrangement or array, from at least 80% of theultrasound sources of the opposed arrangement or array, from at least85% of the ultrasound sources of the opposed arrangement or array, fromat least 90% of the ultrasound sources of the opposed arrangement orarray, from at least 95% of the ultrasound sources of the opposedarrangement or array, from substantially all of the ultrasound sourcesof the opposed arrangement or array, or any other suitable percentage ofultrasound sources of an opposed array. Depending on the number ofultrasound sources of an arrangement, such percentages may represent alarge number of sources. For example, even 0.2% of ultrasound sources ofan arrangement including 1,000 ultrasound sources (i.e., 2 sources outof the 1,000 sources) may represent a sufficient number of ultrasoundsources from which an ultrasound sensor may receive and discriminatebetween distinct signals for purposes of volumetric imaging, as anon-limiting example, particularly where each sensor discriminates twodifferent sources. In some such embodiments, the arrangement ofultrasound sources may include at least fifty ultrasound sources.

Considering absolute numbers, an ultrasound sensor of the apparatus 100may be configured in some non-limiting embodiments to receive, and anapparatus or system comprising apparatus 100 may be configured todiscriminate between, distinct signals from at least three ultrasoundsources of an opposed arrangement or array, from at least fiveultrasound sources of the opposed arrangement or array, from at leastten ultrasound sources of the opposed arrangement or array, from atleast fifty ultrasound sources of the opposed arrangement or array, fromat least 100 ultrasound sources of the opposed arrangement or array,from at least 1,000 ultrasound sources of the opposed arrangement orarray, from at least 10,000 ultrasound sources of the opposedarrangement or array, from between ten and 10,000 ultrasound sources ofthe opposed arrangement or array, from between 100 and 20,000 ultrasoundsources of the opposed arrangement or array, or from any other suitablenumber of ultrasound sources.

Moreover, it should be appreciated that different ultrasound sensors ofthe array 102 b may be configured to receive ultrasound signals fromdifferent percentages of the ultrasound sources of array 102 a. However,as previously described, according to an embodiment, at least someultrasound sensors of the array 102 b may be configured to receivesignals from ultrasound sources of the array 102 a arranged in at leasttwo dimensions. Operation in this manner may provide a relatively largeamount of data about a subject located between the arrays 102 a and 102b, as will be described further below, and therefore may facilitaterapid and accurate 3D data collection and/or imaging of the subject.

As will be described in greater detail below, the apparatus 100 may becoupled to suitable circuitry to facilitate its operation. For example,the apparatus 100 may be coupled to suitable circuitry to discriminatebetween multiple ultrasound signals received by an ultrasound sensorfrom multiple ultrasound sources arranged in at least two dimensions.

While the operation of an apparatus 100 according to some embodiments ofthe present application may take several variations, multiple of whichare described in detail below, a general overview is now provided. Thearrays 102 a and 102 b may be suitably positioned with respect to asubject of interest. For example, if the subject is a patient, thearrays 102 a and 102 b may be suitably positioned in an opposingconfiguration to investigate the patient's abdomen, breast, head, or anyother portion of interest. The ultrasound sources of array 102 a may beconfigured to concurrently (and in some embodiments, simultaneously)transmit ultrasound signals. According to an embodiment, two of more ofthe ultrasound sources may concurrently transmit distinct ultrasoundsignals. In a non-limiting scenario, each ultrasound source may transmita distinct ultrasound signal.

As used herein, the transmission of two signals is concurrent if thesignals have any overlap in time as they are being transmitted.Depending on the context, the transmission of signals is substantiallyconcurrent if overlapping in time by at least 80%, by at least 90%, ormore. In some embodiments, signals may be transmitted generally seriallysuch that a first one or more signals is concurrent with a second one ormore signals, the second one or more signals is concurrent with a thirdone or more signals, etc., even though the third one or more signals mayor may not be concurrent with the first one or more signals. Thetransmission of two signals is substantially simultaneous if overlappingin time by approximately 95% or more.

As will be described further below, not all embodiments involveconcurrent or simultaneous transmission of signals from a plurality ofultrasound sources. The ultrasound sensors of array 102 b may receivethe ultrasound signals sourced by the ultrasound sources of array 102 a.The signals may be discriminated between (e.g., based on code, time,frequency or in any other suitable manner, non-limiting examples ofwhich are described below) and processed to determine properties ofinterest of the patient (or other subject), such as density of tissue,speed of sound in the tissue, and/or index of refraction of the tissue,among other possibilities. One or more images may then be reconstructedbased on such data.

As described, various properties of interest of a subject may bedetermined, as will be described in greater detail below. Determinationof such properties may be made by consideration of characteristics ofthe ultrasound signals received by the ultrasound sensors of array 102b. For example, one or both of attenuation and time-of-flight through asubject of the ultrasound signals may be measured. The attenuation maybe determined, for example, by consideration of the amplitude (and/orpower) of an ultrasound signal received by an ultrasound sensor of thearray 102 b relative to the amplitude (and/or power) of the ultrasoundsignal transmitted by an ultrasound source of the array 102 a. Thetime-of-flight may be determined, for example, by consideration of aphase shift of the transmitted signal induced by passage of the signalthrough the subject.

The measured attenuation and/or time-of-flight of ultrasound signals asdetermined as part of operation of the apparatus 100 may be used tocalculate (or otherwise determine) one or more physical properties ofinterest of the subject. For instance, time-of-flight may be indicativeof speed of sound, and therefore may also provide information aboutdensity and/or temperature within the subject. Attenuation and/or timeof flight may be indicative of the index of refraction within thesubject.

One or both of the arrays may be operated according to beamformingtechniques to form a beam. Beamforming is described in detail below withrespect to operation of HIFU arrays, but may also be applied in thecontext of imaging. For example, beamforming may be applied on thetransmission side (source side) of a system and/or on the receiving sideof the system (termed “receive beamforming” or “receiving beamforming”).Beamforming may facilitate focused evaluation of a point of interestwithin the volume enclosed by the arrays. Beamforming may be used toform any suitable type of beam such as a low aperture beam, sometimescalled a pencil beam, as one example. Various beamforming techniques maybe used, including but not limited to broadband beamforming, dynamicbeamforming, adaptive beamforming, transmit beamforming, and receivingbeamforming Apodization may also be used to augment beamforming, forexample by suitable weighting of signals sent/received by the arrays.Any of the above beamforming techniques may be implemented by usingdigital processing circuitry, analog processing circuitry, or by using acombination of digital and analog processing circuitry.

Operation of an apparatus 100 may provide various benefits in terms ofdata collection and/or imaging, some of which are described in furtherdetail below. For example, high resolution volumetric imaging may beachieved using data collected by an apparatus of the type shown in FIG.1A. Resolution may provide a measure of the smallest volume in which theultrasound imaging device may discern a distinct value of a property(e.g., index of refraction, attenuation, density, temperature, speed ofsound, etc.) of the subject being imaged. The higher the resolution, thesmaller the volume in which such a change may be detected by operatingthe ultrasound imaging device. Resolution on the order of millimeters(e.g., 5 cubic mm or finer, 2 cubic mm or finer, 1 cubic mm or finer,etc. in some non-limiting embodiments) may be achieved by suitablespacing of ultrasound elements in the imaging device. Such resolutionmay be achieved for various volumes and, for example, may be achievedfor volumes on the order of 0.1-1 cubic mm, 1-10 cubic mm, 10-100 cubicmm, 100 cubic mm-1 cubic cm, 1-10 cubic cm, 10-25 cubic cm, 25-200 cubiccm, 200-500 cubic cm, 500-1000 cubic cm, 1000-2500 cubic cm, etc., insome non-limiting embodiments. As the volume being imaged gets smaller,imaging that volume at a higher resolution may be possible.

It should be appreciated that although, in some embodiments, avolumetric image may comprise voxels having a volume approximately thesame as the resolution of the ultrasound imaging device (e.g., thevolume of each voxel in the volumetric image is approximately 5 cubic mmwhen the resolution of the ultrasound imaging device is approximatelycubic 5 mm), aspects of the present application are not limited in thisrespect. For example, in some embodiments, the volume of one or morevoxels in a volumetric image may be smaller than the resolution of theultrasound imaging device.

Rapid operation of the apparatus 100 may also be provided. For example,data collection corresponding to each source transmitting a signal andeach sensor receiving the signal may be performed at a rate ofapproximately up to 5 frames per second, up to 10 frames per second, upto 25 frames per second, up to 50 frames per second, up to 75 frames persecond, up to 100 frames per second, up to 125 frames per second, or anyother suitable rate. Thus, as a non-limiting example, data collectioncorresponding to each source transmitting a signal and each sensorreceiving the signal may be collected in less than approximately 0.5second, less than approximately 300 milliseconds, less thanapproximately 200 milliseconds, or at any other suitable rate. The ratemay depend, at least partially, on the number of sources and sensors ofthe apparatus.

Reconstruction of volumetric images using data collected with apparatus100 may also be performed rapidly. Due to the high speeds of datacollection possible with apparatus of the type described, volumetricimages may be reconstructed at a rate up to approximately six volumetricimages/second, as a non-limiting example. In some embodiments, real timevolumetric imaging may be provided.

Another benefit that may be realized from use of an apparatus 100 ishigh signal fidelity. As described, the apparatus 100 of FIG. 1A may beused to collect large amounts of data in relatively short time periods.For example, in embodiments where the arrays 102 a and 102 b have N×Nultrasound elements, a single scan with the apparatus 100 may produce onthe order of N⁴ distinct measurements. A scan represents a singleactivation and collection of data from a group of elements (sometimesrepresenting all elements of a system and other times representing asubset), and thus results in collection of a frame of data. N is four inthe non-limiting example of FIG. 1A, but may be any suitable number,examples of which have been previously given, and which may includetens, hundreds, or thousands of ultrasound elements. For example,according to some embodiments arrangements of ultrasound elementsconfigured to perform ultrasound imaging may include, as non-limitingexamples, at least three ultrasound elements, at least ten ultrasoundelements, at least twenty-five ultrasound elements, at least fiftyultrasound elements, at least 100 ultrasound elements, at least 1,000ultrasound elements, or any other suitable number. In the non-limitingexample of FIG. 1A, the array 102 a is an N×N array, but not allembodiments are limited to arrays having sides of equal dimension. Forexample, one or both of the arrays may be N×M arrays, where N and Mdiffer. However, for ease of explanation, it is currently assumed thearrays are N×N arrays.

As described previously, the apparatus 100 may be operated such that, insome embodiments, each ultrasound sensor receives a distinct signalsourced by each ultrasound source. Distinct signals may be signals thatare distinguishable (i.e., that the processing circuitry candiscriminate), at least in part, on the basis of content of the signals,the times at which the signals are sent, the elements transmitting thesignals, the elements receiving the signals, the channel over which thesignals are transmitted, etc. Therefore, in the non-limiting example ofFIG. 1A, each ultrasound sensor of array 102 b may receive up to N×N=N²distinct ultrasound signals per scan, which signals may have beenproduced concurrently by the N×N sources in some non-limitingembodiments (though not all embodiments are limited in this respect).Considering that the array 102 b itself includes N×N=N² ultrasoundsensors, a single scan with the apparatus 100 may result in N⁴ distinctmeasurements. More generally, in some embodiments, an N×M arrangement ofradiation sources emitting respective source signals to an X×Yarrangement of radiation sensors may provide for receipt of, anddiscrimination between (e.g., using suitable processing circuitry)greater than X×Y×N received signals from the N×M radiation sources. Insome embodiments, up to (X×Y×N×M) respective signals may be received bythe X×Y arrangement of radiation sensors from the N×M arrangement ofradiation sources, and in some embodiments discrimination may beprovided between approximately (X×Y×N×M) respective signals. In somenon-limiting embodiments, N=M=X=Y. Such large numbers of measurementsmay improve signal fidelity and/or facilitate real time imagingfunctions (e.g., generation of 3D images), real time thermometryfunctions (e.g., generation of 3D temperature profiles), or otherdesirable functions.

The provision of N⁴ measurements using the apparatus 100 of FIG. 1A isto be contrasted with the number of measurements which could be achievedby operating an apparatus in a slice-based (“tomographic”) modality inwhich sensors can sense signals only from sources of a singleone-dimensional row. Although operation of an apparatus in such a mannermay allow for generation of 3D images by stacking “slices,” the amountof data obtained from slice-based approaches is significantly less andthe need to generate multiple slices can take significantly more time.Thus, operation of the apparatus 100 in the manner described above, inwhich ultrasound sensors may receive distinct signals from ultrasoundsources arranged in at least two dimensions (and for which the signalsmay be discriminated, for example using suitable processing circuitry)may provide a significant increase in the number of measurements whichmay be made per scan and/or the timeframe within which they can be madecompared to a slice-based approach.

Furthermore, it should be appreciated from that in some embodiments theapparatus 100 of FIG. 1A may be used to achieve volumetric imaging of asubject without the need to mechanically scan the arrays of ultrasoundelements. Rather, the arrays may be maintained in a static relationshipwith respect to each other according to some aspects, while stillproviding data suitable to reconstruct a volumetric representation of asubject, and again without using slice-based techniques. The ability tomaintain the arrays static relative to each other during operation mayfacilitate rapid collection of data, since mechanical scanning ofultrasound elements would, in many if not all situations, require moretime than electrical excitation of different elements of the arrays. Forexample, the time needed to emit distinct signals from each of theultrasound elements 104 of array 102 a may be significantly less thanthe time which would be needed to mechanically scan a row of ultrasoundelements across the distance occupied by the array 102 a.

The prior description has assumed that ultrasound elements 104 of arrays102 a are configured as ultrasound sources and that ultrasound elements104 of arrays 102 b are configured as ultrasound sensors. However, aspreviously described, the apparatus 100 is not limited to the ultrasoundelements 104 of the arrays 102 a and 102 b being limited to performing asingle function. Rather, according to a non-limiting embodiment, theultrasound elements 104 of arrays 102 a and 102 b may be configured tooperate as both ultrasound sources and sensors, or may be configured toexhibit time-varying functionality. For example, in a non-limitingembodiment, the ultrasound elements 104 of array 102 a may be configuredto operate as ultrasound sources during a first time interval and asultrasound sensors during a second time interval. The ultrasoundelements 104 of array 102 b may be configured to operate as ultrasoundsensors during the first time interval and as ultrasound sources duringthe second time interval, as a non-limiting example. Thus, the operationof the ultrasound elements 104 may vary with time. A non-limitingexample is described below with respect to FIG. 6B.

As described, according to an aspect of the present application, anapparatus of the type illustrated in FIG. 1A may be coupled to suitablecircuitry (or other components), for example as part of a system. Thecircuitry may facilitate operation of the apparatus 100 in any of themanners previously described. A non-limiting example is shown in FIG. 2in the form of system 200.

As shown, the system 200, which may be considered an imaging system insome embodiments, comprises front-end circuitry 202 coupled to theapparatus 100 of FIG. 1A, and more particularly to the array 102 a, aswell as front-end circuitry 204 coupled to the apparatus 100, and moreparticularly to the array 102 b. Front-end circuitry 202 and front-endcircuitry 204 may be distinct circuitry in some embodiments or may bethe same in other embodiments. According to one embodiment, thefront-end circuitry 202 and front-end circuitry 204 may in combinationform a single control circuit. The front-end circuitry 202 and front-endcircuitry 204 may be any suitable circuitry for controlling operation ofthe apparatus 100 and processing data produced by the apparatus 100. Asused herein, front-end circuitry may include circuitry which interfaceswith arrangements of radiation elements. Non-limiting examples aredescribed below.

While apparatus 100 is illustrated as being part of the system 200, itshould be appreciated that systems of the type illustrated are notlimited to using opposed array configurations of the type shown in FIG.1A. Rather, the inclusion of apparatus 100 in FIG. 2 is done for thepurposes of illustration, and variations are possible, as will bedescribed in greater detail below.

The front-end circuitry 202 may control generation of signals (e.g.,ultrasound signals) to be sourced by the apparatus 100, for example fromthe array 102 a. As described previously, according to one mode ofoperation the signals may be transmitted from the array 102 a to thearray 102 b, the elements of which may operate as sensors. The front-endcircuitry 204 may process the signals received by the elements 104 ofarray 102 b in any suitable manner For example, as will be described ingreater detail below, the front-end circuitry 204 may perform one ormore of filtering, amplifying, digitizing, smoothing, and/or otherconditioning of the received signals. The front-end circuitry 204 mayanalyze the received signals to determine characteristics such as one ormore of time of arrival, phase, amplitude, frequency, and/or othercharacteristics of interest. The front-end circuitry 204 mayadditionally or alternatively determine one or more properties ofinterest of a subject based on the received signals, such as speed ofsound in the subject, index of refraction in the subject, density of thesubject, and/or temperature, among others. The front-end circuitry 204may, in some embodiments, control generation of volumetric images basedon data determined from the signals received by the array 102 b.

FIG. 3 illustrates a flowchart of an example of the operation of thesystem 200 of FIG. 2, according to a non-limiting embodiment. The methodof operation 300 may begin at 302 with generation of the signals (e.g.,ultrasound signals or any other suitable signals) to be transmitted, forexample by the array 102 a of ultrasound elements 104. The generatedsignals may then be transmitted at 304 from one or more of theultrasound elements, for example from one or more of the ultrasoundelements 104 of the array 102 a. As will be described in greater detailbelow, the transmission of signals may be performed in any suitablemanner, such as using code division multiplexing, time divisionmultiplexing, frequency division multiplexing, a combination of two ormore of these multiplexing techniques, or in any other suitable manner.

At 306, the transmitted signals may be received by one or more of theultrasound elements 104, for example by one or more of the ultrasoundelements 104 of the array 102 b. Depending on the manner in which thesignals were transmitted at 304, the reception of signals at 306 mayoccur concurrently for multiple ultrasound elements configured assensors, may occur substantially simultaneously, or may occur atdifferent times for different ultrasound elements 104 configured assensors.

At 308, the received signals from 306 may be processed in any suitablemanner. For example, the signals may be processed in any of the mannersdescribed above (e.g., filtering, amplifying, digitizing, smoothing,etc.) or in any other suitable manner, as the aspects of the applicationare not limited in this respect.

At 310, one or more volumetric images may be reconstructed based atleast in part on the signals received at 306 and processed at 308. Itshould be appreciated that any one, any two or all three acts 306, 308,and/or 310 may be performed in real time. For example, in someembodiments, signals may be received in real time at 306, processed inreal time at 308, and used to reconstruct one or more volumetric imagesin real time at 310. In other embodiments, signals may be received inreal time at 306, processed in real time at 308, but used to reconstructone or more volumetric images at a later time at 310. In yet otherembodiments, signals may be received in real time at 306, but processedat a later time at 308 and afterward used to reconstruct one or morevolumetric images at 310.

Regardless of whether volumetric images are reconstructed in real-timeor offline, when multiple volumetric images of a subject being imagedare obtained, in some embodiments, the obtained volumetric images may beprocessed to produce a sequence or movie of volumetric images. Forexample, if the subject being imaged is in motion (e.g., a fetus, anorgan of a patient such as a heart, kidney, breast, ovary, etc.,) amovie of the subject undergoing motion (e.g., a movie of a heartbeating, a movie of a fetus moving, etc.) may be created.

FIG. 4 illustrates a non-limiting example of an embodiment of the system200 of FIG. 2. As shown, the system 400 may include opposed arrays 402 aand 402 b of ultrasound elements positioned on opposite sides of asubject 410, and defining a volume 418 therebetween. The system 400 mayfurther comprise front-end circuitry (e.g., front-end circuitry 202 orany other suitable front-end circuitry) comprising a user interface 404,a control system 406, and a transmitter 408 configured on the front-endof opposed arrays 402 a and 402 b. The user interface may be anysuitable user interface, including but not limited to a computerinterface with which the user may interact visually (e.g., a screen, atouchscreen, etc.), verbally, via remote control, or in any othersuitable manner.

According to a non-limiting embodiment, the user (e.g., a technician,doctor, investigator, or any other user) may control operation of thesystem 400 via the user interface. As a non-limiting example, one ormore pre-programmed imaging routines may be available to the system, andmay be stored in the system in suitable computer memory. Such routinesmay relate to aspects of the operation of the system 400 such asduration of operation, number of scans to perform, type of scan toperform, etc. For example, the user may select a pre-programmed imagingroutine via the user interface. Alternatively, the user may create animaging routine via the user interface. Others controls of the system400 may also be provided via the user interface.

The control system 406 may control generation of signals to be sent byultrasound elements of one or both of the opposed arrays 402 a and 402b. The control system may include any suitable circuitry. For example,according to a non-limiting embodiment, the control system may be afield programmable gate array (FPGA). However, alternatives arepossible, including at least one general-purpose processor, as anon-limiting example. The control system may operate in any suitablemanner, for example by executing a computer program of other executableinstructions governing its operation. The control system may thereforecontrol operation of the system to perform imaging functions (e.g.,collecting one or more images), HIFU functionality (described in greaterdetail below), or a combination of the two.

The transmitter 408 may perform any suitable functions for transmittingthe signals generated by the control system 406 from the ultrasoundelements of the opposed arrays 402 a and 402 b. For example, thetransmitter 408 may include one or more amplifiers, one or more filters,and/or one or more digital-to-analog converters, as non-limitingexamples. The transmitter 408 may include distinct circuitry for one ormore (and in some embodiments, each) ultrasound element of the array 402a, though not all embodiments are limited in this manner For instance,the transmitter 408 may additionally or alternatively include circuitryshared among two or more (e.g., all) ultrasound elements of the array402 a. Non-limiting examples of suitable transmitting circuitry aredescribed in further detail below.

The system 400 also includes a receiver 412, pre-processing circuitry414, and reconstruction computer 416. The receiver 412 may comprisecircuitry suitable for, for example, conditioning the received signalsdetected by ultrasound elements (e.g., of the array 402 b) configured asultrasound sensors. For example, the receiver 412 may includeamplifiers, filters, one or more analog to digital converters, and/orany other suitable circuitry. According to an embodiment, the receiver412 includes distinct circuitry for one or more (and in someembodiments, each) ultrasound elements of the array 402 b. Additionallyor alternatively, the receiver 412 may include circuitry shared amongtwo or more ultrasound elements of the array 402 b.

The pre-processing circuitry 414 may perform one or more functions onthe received signals in addition to those performed by the receiver 412,such as determining one or more characteristics of the received signals.As non-limiting examples, the pre-processing circuitry 414 may performmatched filtering, correlation (e.g., as described further below withrespect to pulse compression), and/or may detect an amplitude of areceived signal, a phase of the received signal, and/or a frequency ofthe received signal, among other signal characteristics. Other functionsmay additionally and/or alternatively be performed, as those listedrepresent non-limiting examples. Further details are provided below. Insome embodiments, receiver 412 and pre-processing circuitry 414 may becombined and their functions performed by the same circuitry orcomputer.

The reconstruction computer 416 may receive data from the pre-processingcircuitry and reconstruct one or more volumetric images (orthree-dimensional temperature profiles, described further below withrespect to FIG. 40) of the subject 410, non-limiting examples of whichwill be shown and described below. Additionally or alternatively, thereconstruction computer 416 may receive data from control system 406.The reconstruction computer 416 may be any suitable computer and mayutilize any suitable reconstruction process(es), as aspects of theinvention described herein are not limited in this respect. As onenon-limiting example, in some embodiments, one or more compressivesensing techniques may be utilized to reconstruct one or more volumetricimages of data collected by an ultrasound imaging system. Thereconstruction computer 416 may, therefore, implement one or morecompressive sensing techniques according to some embodiments. As anothernon-limiting example, in some embodiments, one or more algebraicreconstruction techniques may be utilized to reconstruct one or morevolumetric images of data collected by an ultrasound imaging system. Thereconstruction computer 416 may, therefore, implement one or morealgebraic reconstruction techniques according to some embodiments.

While the reconstruction computer 416 is illustrated as a singlecomputer, it should be appreciated that the various aspects describedherein in which volumetric images are reconstructed are not limited inthis manner Rather, reconstruction of a volumetric image (or multiplevolumetric images) may be performed by two or more computers, servers,graphical processing units, and/or other processors. For example, thereconstruction computer 416 may include two or more computers whichperform distinct steps of a reconstruction process. Alternatively, thereconstruction computer 416 may include two or more computers whichperform one or more common reconstruction functions in parallel. Thereconstruction computer (or other reconstruction hardware) may belocated local to the other components of the system 400, may be locatedremotely, or may include some hardware located locally and some locatedremotely. If reconstruction hardware is located remotely, communicationbetween the reconstruction hardware and the pre-processing circuitry maybe performed in any suitable manner, including wirelessly, via a wiredconnection, via the internet, via a cloud (as in cloud computing), or inany other suitable manner Moreover, it should be appreciated that thefunctionality of the reconstruction computer 416 and the receiver 412and/or pre-processing circuitry 414 may be performed by a single unit,e.g., a single processor. For example, a single processor may performthe functionality of 412, 414, and 416. Thus, it should be appreciatedthat in some embodiments a single processor may function to receive anddiscriminate signals sensed by radiation sensors and create a 3D imageand/or 3D temperature profile based on the received and discriminatedsignals. Alternatively, such functionality may be divided betweenmultiple hardware units in any suitable manner.

As described previously, in some embodiments a sensor, such as a sensorof array 402 b, may be configured to receive signals originating frommultiple sources whose positions define a substantial solid angle withrespect to each sensor, such as, for example, a solid angle of at leastπ/10 steradians, at least π/5 steradians, at least π/4 steradians, atleast π/2 steradians, at least π steradians, at least 2π steradians,between approximately π/10 and 2π steradians, between approximately π/5and it steradians, or any other suitable non-zero solid angle. Anon-limiting example is shown in FIG. 4 with respect to solid angle 420.As shown, a single sensor may be configured to receive signalsoriginating from sources occupying the solid angle. Namely, non-zerosolid angle 420 has a vertex V₄₂₀ located on a sensor of array 402 b(e.g., on the center point of the sensor). The solid angle 420encompasses eight elements of the array 402 a in the illustratednon-limiting example, and thus the sensor defining the vertex of thesolid angle 420 is configured to receive signals emitted by at leasteach of the eight elements of the array 402 a encompassed by the solidangle. The solid angle 420 may have any of the values previously listedherein for solid angles, or any other suitable value.

In some embodiments, sensors of an array may be configured to definemultiple different solid angles with respect to sources of an opposedarray. For example, FIG. 4 illustrates a non-zero solid angle 422 inaddition to the non-zero solid angle 420. The non-zero solid angle 422has a vertex V₄₂₂ located on a different sensor of the array 402 b thanthat on which the vertex V₄₂₀ of solid angle 420 is located. In thenon-limiting example illustrated, solid angle 422 includes the sameeight elements of array 402 a as solid angle 420. The solid angles aredistinct, however, since their vertices are aligned on different sensorsof the array 402 b.

Generally, then, it should be appreciated that embodiments of thepresent application provide apparatus in which sensors of an arrangementare configured to receive signals emitted from sources defining multipledifferent solid angles with respect to the sensors. Such a geometry mayallow for collection of large amounts of data from the source-sensorarrangement, without the need to mechanically scan the arrangement andin a relatively short period of time. For example, much more data may becollected with such a geometry than that allowed by slice-based imagingsystems.

The components in FIG. 4 may be coupled in any suitable manner,including wired and/or wireless connections. In some embodiments, highspeed connections may be used to facilitate collection and processing oflarge amounts of data, as may be desired in various imagingapplications. According to an embodiment, the arrays 402 a and/or thearray 402 b may be coupled to the processing circuitry via aThunderbolt™ interface, fiber-optics, Rocket IO™ from Xilinx Inc. of SanJose, Calif., or other high-speed interface.

The operation of one or more components of system 400 may besynchronized according to a non-limiting embodiment. Suchsynchronization may be achieved in any suitable manner According to anembodiment, a common clock may be distributed to one or more of thevarious components of system 400 which utilize clock signals. Forexample, in some embodiments, a common clock may be distributed to theone or more digital-to-analog converters and analog-to-digitalconverters in system 400. Additionally, a common clock may bedistributed to one or more FPGAs in system 400. Alternatively, multiplesynchronized clocks may be provided to appropriate components of thesystem 400. Thus, the various aspects of the present application are notlimited to synchronizing the operation of components in any particularmanner As another example, one or more phase-locked loops may be used tosynchronize operation of components of the system 400. Moreover, itshould be appreciated that such synchronization is not limited to theconfiguration of FIG. 4, but may be implemented in any of the systemsdescribed herein.

In some embodiments, ultrasound elements, such as those shown in FIG. 4and the other figures herein, may be integrated with correspondingcircuitry. For example, referring to FIG. 4 as a non-limiting example,the transmitter 408 may be integrated with the array 402 a and/or thereceiver 412 may be integrated with the array 402 b. The components maybe integrated on a single substrate, for example by flip-chip bonding,flex-circuit bonding, solder bump bonding, monolithic integration, or inany other suitable manner. As an example, the transmitter 408 may bemonolithically integrated on a same substrate as the ultrasound elementsof array 402 a. Alternatively, the transmitter 408 may be formed on afirst substrate and flip-chip bonded to a substrate on which theultrasound elements of array 402 a are formed. Examples of suitabletransmit circuitry and receive circuitry are described in greater detailbelow (e.g., see FIGS. 7, 9, 10, and 11A-11D), and representnon-limiting examples of circuitry which may be integrated withultrasound elements of one or more arrays. In some embodiments, thesubstrate may be acoustically insulating, and thus formed of anysuitable acoustically insulating material.

A system like that in FIG. 4, as well as the other systems describedherein, may be operated in a manner to provide beamforming functionalityfrom one or more arrays. Beamforming may be valuable in the imagingcontext to facilitate focused imaging of a desired part of a subject.Beamforming may be applied on the transmission side (source side) of asystem and/or on the receiving side of the system.

When beamforming is used, various beamforming techniques may be applied.In some embodiments, broadband beamforming may be implemented. In suchembodiments, coded signals may be transmitted on top of a singlefrequency, as a non-limiting example. Non-linear chirps represent oneexample of suitable waveforms that may be transmitted in the beamformingcontext. If beamforming is to be performed on a receiving side of thesystem (by an array like array 402 b in FIG. 4), suitable techniques mayinclude Fourier resampling and/or delay and sum techniques, and may beperformed in analog or digital domains If beamforming is to be performedon the transmitting side of the system (by an array like array 402 a inFIG. 4), analog signal delay processing and/or digital signal delayprocessing may be implemented. In the analog domain, a single waveformmay be delayed using suitable delay circuitry. In the digital domain,delay processing may involve using multiple waveforms. Other techniquesmay also be used.

In some embodiments, beamforming may be augmented by use of apodization,for example by weighting signals transmitted and/or received in anysuitable manner to reduce sidelobes. Any suitable implementation ofapodization to achieve a desired type and degree of beamforming may beimplemented.

In some embodiments, time-reversal beamforming may be used in theimaging context. For example, time reversal beamforming may be valuablewhen imaging fatty tissue.

When beamforming is used, any suitable type of beam may be formed.Examples of beams that may be formed include, but are not limited to,Bessel beams, plane waves, unfocused beams, and Gaussian beams. Othertypes of beams are also possible. The type of beam formed may depend, insome embodiments, on the geometry of the imaging configuration. Forexample, depending on the shape of the subject and the configuration ofultrasound elements, a particular beam type may be chosen.

As described, the system 400 of FIG. 4 represents a non-limitingimplementation of a system of the type illustrated in FIG. 2. Analternative implementation is illustrated in FIG. 5 as system 500. Asshown, the system 500 includes transmit circuitry 502, an FPGAcorrelator 504, and receive circuitry 506. The FPGA correlator 504 isconfigured to generate and provide to the transmit circuitry 502 signalsfor transmission from one or more ultrasound elements (e.g., of thearray 402 a). The receive circuitry 506 is configured to receive signalsdetected by one or more ultrasound elements (e.g., of the array 402 b)and provide received signals to the FPGA correlator 504 for furtherprocessing (e.g., correlation of the signals, etc.). The FPGA correlator506 provides its output to the reconstruction computer 416, which mayoperate in the manner previously described with respect to FIG. 4.

FIG. 6A illustrates another embodiment of a system of the typeillustrated in FIG. 2. The system 600 of FIG. 6A includes a display andgraphical user interface (GUI) 602 via which a user may inputinformation to the system (e.g., selections of imaging parameters,operating schemes, pre-programmed imaging routines, and/or othersuitable information) and/or view output data and images. The system 600further comprises a reconstruction process 604 and pre-processing block606. The reconstruction process, which may be stored by any suitablecomputer readable media and executed by any suitable hardware (e.g., acomputer, such as a reconstruction computer), may receive data from thepre-processing block 606 and generate one or more reconstructions (e.g.,reconstructed images). For example, the reconstruction process 604 maybe used to generate one or more volumetric images of the subject 410, ina non-limiting embodiment. The pre-processing block may perform anysuitable processing on signals received (e.g., by the array 402 b) andinitially processed by the receiver 412 and analog to digital converter(ADC) 610. For example, the pre-processing block 606 may perform thefunctions previously described with respect to pre-processing circuitry414, or any other suitable functions.

In some embodiments, the pre-processing block 606 may provide initialdigital waveforms to the digital to analog converter (DAC) 608. The DACmay then generate one or more analog signals to be transmitted from thearray 402 a using the transmitter 408. Although only a single signalchain is illustrated in system 600 for both the transmit and receiveportions of the system, it should be appreciated that the system mayalternatively include a respective transmit chain (one or moretransmitter components) for each of two or more ultrasound elements ofthe arrays 402 a and a respective receive chain (one or more receivercomponents) for each of two or more ultrasound elements of the array 402b. In some embodiments, a respective signal transmit chain may beprovided for each ultrasound element of the array 402 a and a respectivesignal receive chain may be provided for each ultrasound element of thearray 402 b.

As described previously, in some embodiments one or more ultrasoundelements of an arrangement may be configured to exhibit time-varyingoperation as a source and sensor. FIG. 6B illustrates an example of asuitable configuration for achieving such operation. The system 650 ofFIG. 6B differs from the system 600 of FIG. 6A in that the array 402 ais additionally coupled to a switch 652, a receiver 654, and an ADC 656.In this manner, the ultrasound elements of array 402 a may be configuredto operate both as ultrasound sources and ultrasound sensors. To operatethe array 402 a as a transmitting array, the switch 652 (which may beany suitable type of switch) may couple the array 402 a to thetransmitter 408, in which case the array 402 a operates as previouslydescribed herein. To operate the array 402 a as a receiving array, theswitch 652 couples the array 402 a to the receiver 654, which mayoperate in the manner previously described herein with respect toreceiver 412. The ADC 656 may operate in the manner previously describedwith respect to ADC 610. Thus, suitable (time-varying) operation of theswitch 652 may provide desired time-varying operation of the array 402a.

FIGS. 7A-7C illustrate non-limiting implementations of a signal transmitchain (also referred to as a transmitter) in accordance with one or moreaspects of the present application, as may be used to transmitultrasound signals from an ultrasound element. Thus, FIGS. 7A-7Cillustrate non-limiting examples of signal transmit chains as may beused in systems of the types illustrated in FIGS. 2-6, or any othersuitable systems. The signal chains may be linear in some embodiments.In each FIG. 7A-7C, only a single signal transmit chain is illustrated.Such a signal transmit chain may be shared among two or more ultrasoundelements of an array (e.g., array 402 a) or may be dedicated to a singleultrasound element of an array. According to a non-limiting embodiment,a respective signal transmit chain of the types illustrated may bededicated to each ultrasound element configured as an ultrasound source.

The signal transmit chain 700 a of FIG. 7A includes a waveform generator701 and an amplification stage 705 coupled to the array 402 a. Thewaveform generator 701 may be any suitable type of waveform generatorfor generating signals of the type to be sent from ultrasound elementsof the opposed arrays. Thus, the waveform generator 701 may be an analogor digital waveform generator.

The waveforms to be generated by the waveform generator 701 may have anysuitable frequency. For example, according to aspects of the presentapplication, one or more systems of the types described herein may beconfigured to transmit and receive ultrasound signals having frequenciesin a range from approximately 1 MHz to approximately 10 MHz, fromapproximately 3 MHz to approximately 8 MHz, or from approximately 4 MHzto approximately 7 MHz. The listed frequency ranges are non-limitingexamples, as alternative frequency ranges are also possible. Accordingto some embodiments, the signals may be broadband signals, which may bebeneficial to spread the power of the signals across a frequency range.In some embodiments, the signals may have center frequencies ofapproximately 2.5 MHz, or approximately 5 MHz as non-limiting examples,with a bandwidth of approximately 50% of the center frequency.

The type of waveform generated by waveform generator 701 may depend, atleast partially, on the desired use of the signals and therefore thedesired characteristics of the signals to be transmitted by theultrasound elements. For example, as described, it may be desirable toutilize a wideband waveform rather than a narrowband (or, in theextreme, a single frequency) waveform. Use of a wideband waveform maymake more practical the attainment of high power signals, since thepower may be spread across frequencies rather than concentrated at asingle frequency. Also, as previously described with respect to FIG. 1A,in at least one embodiment it may be desirable for a system todistinguish (or discriminate) between multiple ultrasound signalsreceived by a single ultrasound sensor from multiple ultrasound sources.Thus, it may be desirable in at least some circumstances for the signalgenerated by the waveform generator 701 to be of a type which may bedecoded on the receiving end of the system, for example using a matchedfilter or any other suitable decoding technique.

As a non-limiting example, the waveform generated by waveform generator701 may be a wideband waveform. The wideband waveform may have a centerfrequency chosen to substantially correspond to a center frequency of anultrasound element from which the waveform will be sent (e.g., theultrasound elements of array 402 a) and having a bandwidth in suitableproportion to a bandwidth of the ultrasound element. For example, thebandwidth of the waveform may be selected to be approximately 100% ofthe bandwidth of the ultrasound elements from which it will betransmitted, may be selected to be approximately 75% of the bandwidth ofthe ultrasound elements from which it will be transmitted, may beselected to be approximately 50% of the bandwidth of the ultrasoundelement from which it will be transmitted, may be selected betweenapproximately 40% and approximately 60% of the bandwidth of theultrasound element from which it will be transmitted, or may have anyother suitable relationship to the bandwidth of the ultrasound element,as the numbers listed are non-limiting examples.

Waveform generator 701 may generate any of numerous types of widebandwaveforms. One non-limiting example of a wideband waveform is a chirp.The chirp may be generated to have any suitable characteristics. Forexample, the chirp may be a linear chirp whose instantaneous frequencychanges linearly over time. FIG. 8A illustrates a non-limiting exampleof a linear chirp waveform 802. As another example, the chirp may benon-linear chirp whose instantaneous frequency changes non-linearly overtime (e.g., geometrically, logarithmically, or in any other suitableway). In some non-limiting embodiments, the edges of the chirp may beamplitude modulated by the application of a window (e.g., a Hammingwindow, a Hanning window, a Chebyshev window, a prolate-spheroidalwindow, a Blackmann-Tukey window, etc.) to reduce the presence ofsidelobes in the corresponding received waveform.

The chirp may have any suitable duration. The duration may be selected,for example, to provide balance between competing constraints ofsignal-to-noise ratio (SNR) and power. The greater the chirp duration,the greater the SNR, but the greater the average power carried by thesignal. In certain applications, such as imaging of human patients,limits on power deposition may be set which may factor into the desiredpower of a signal generated by the waveform generator. For example, inultrasound imaging applications, guidelines or regulations (e.g., thoseset by the FDA, National Electrical Manufacturers Association, NEMA®,etc.) may place limits on power deposited in a patient. A balancebetween such considerations as power deposition and SNR may be guideselection of a chirp duration. As a non-limiting example, the chirp mayhave a duration of less than 200 microseconds, less than 100microseconds (e.g., approximately 80 microseconds, approximately 70microseconds, approximately 50 microseconds, or any other suitablevalue), less than approximately 50 microseconds, or any other suitablevalue.

In some embodiments, a chirp may be generated as part of a pulsecompression technique employed by the ultrasound imaging device. Pulsecompression may be used to achieve balance between the above-describedcompeting constraints of signal-to-noise ratio (SNR) and power. Insteadof transmitting a narrowband (e.g., a single-frequency sinusoid) signalat a desired power level, the power being concentrated at thefrequencies of the narrowband signal (e.g., the frequency of thesinusoid), a pulse compression technique may comprise transmitting awideband waveform (e.g., a chirp), so that the power is spread over thefrequencies in the wideband waveform (e.g., over the frequencies in arange swept by the chirp). As described in more detail below, a pulsecompression technique further comprises using a pulse compression filterto process the transmitted wideband waveform upon its receipt by one ormore ultrasound sensors. The pulse compression filter may be a matchedfilter that is matched to the transmitted waveform. Though, it should berecognized that the application of a pulse compression technique is notlimited to transmitting chirps as any of numerous other waveforms may beused for pulse compression, as known in the art. For example, phasemodulated waveforms rather than linear or non-linear frequency modulatedwaveforms may be used for pulse compression.

As described, a chirp is a non-limiting example of a wideband waveform,which may be used according to one or more non-limiting embodiments ofthe present application. An alternative includes an impulse, an exampleof which is shown as impulse 804 in FIG. 8B. An impulse may bebeneficial in terms of simplifying detection on a receiving end (e.g.,by ultrasound elements of array 402 b configured as sensors), but mayrequire significant instantaneous power output for generation.

Another example of a class of wideband waveforms, which may be usedaccording to one or more non-limiting embodiments of the presentapplication, are binary waveforms. Binary waveforms may be derived frombinary sequences having suitable time localization properties (e.g.,having a narrow auto-correlation function) and may be obtained in anysuitable manner Examples of suitable binary waveforms include, but arenot limited to, linear maximum length codes (LML codes), Barker codes,and other pseudo-random codes. A binary waveform may be obtained from abinary sequence in any suitable way. For example, in some embodiments, abinary waveform may be obtained by arranging a sequence of impulses intime with the polarity of each impulse being derived from the binaryvalue of the corresponding element in the binary sequence. Other ways ofobtaining binary waveforms from binary sequences include convolving asequence of impulses (e.g., such as the above-described sequence ofimpulses) with any suitable ‘interpolation’ waveform. Examples of such‘interpolation’ waveforms include, but are not limited to, box-carfunctions, triangle functions, sinusoidal pulses, sinc functions, or anyfunction modeling the impulse response of a system, such as, forexample, a measurement system including front-end circuitry, radiationsources, and signal transmission medium. FIG. 8C demonstrates an exampleof such a waveform derived from a binary sequence by using a box-carinterpolation waveform.

Another class of binary waveforms include complementary sequences, orGolay codes. Such codes comprise pairs of sequences sometimes termed‘complementary pairs.’ Each of the sequences in a complementary pairtypically satisfies the time localization properties desired in a binarysequence. The complementary pairs have the additional property thattheir respective autocorrelation functions (i.e., the pulse compressedwaveform) may be additively combined to form a signal with reducedsidelobes. Utilizing such codes may comprise transmitting two distinctpulses for each measurement and combining them after matched filteringin the processing circuitry.

In considering the use of wideband signals, it should be noted thatsignals of different frequency may interact differently with a subject.For example, attenuation of ultrasound signals in a subject may befrequency dependent. Similarly, index of refraction in a subject may befrequency dependent. Other properties of a subject may also be frequencydependent. Thus, according to an aspect of the present application,signals of different frequency may be used to analyze a subject (e.g.,by an apparatus of the types described herein), thus providing different(and in some cases, more) information than may be obtained by usingsignals of only a single frequency. Such operation is not limited to theuse of wideband signals.

It should be appreciated that some embodiments of the presentapplication are not limited to using wideband waveforms. In someembodiments, additionally or alternatively, narrowband waveforms may beused. In one non-limiting illustrative example, a sinusoid having asingle fixed frequency may be used. Such a fixed-frequency sinusoid isan example of a continuous waveform that may be transmitted by one ormultiple ultrasound elements. Such continuous waveforms may be used tocalculate values of one or more properties of the subject being imagedat one or more frequencies. Such a mode of operation may be advantageousin that the measurement of properties of a subject (e.g., index ofrefraction, attenuation, etc.) may depend on the frequency of thewaveform. It should be appreciated that the above-described examples ofwaveforms are provided for purposes of illustration, and thatalternative waveform types may be implemented.

The amplification stage 705, which is coupled to the output of thewaveform generator 701, may be configured to amplify the signalsgenerated by the waveform generator 701 in preparation for theirtransmission from the array 402 a, as a non-limiting example. Also, theamplification stage 705 may perform one or more functions in addition toamplification, including, for example, filtering. In an embodiment, theamplification stage 705 may include a single amplifier and/or a singlefilter. In an embodiment, the amplification stage 705 may includemultiple amplifiers and/or multiple filters, as the various aspectsdescribed herein implementing an amplification stage in a signaltransmit chain are not limited to utilizing any particular amplificationstage.

FIG. 7B illustrates a signal transmit chain 700 b representing anon-limiting, more detailed example of a manner of implementing thesignal transmit chain 700 a of FIG. 7A, providing an example of awaveform generator and an amplification stage. The signal transmit chain700 b includes an arbitrary waveform generator 718. The arbitrarywaveform generator 718 may be a digital waveform generator and may beconfigured to produce any suitable arbitrary waveform(s) of any suitablefrequencies, such as those described above or any other suitablefrequencies. The output of the arbitrary waveform generator 718 isprovided to a digital-to-analog converter (DAC) 704, the output of whichis provided to the amplification stage 705. The DAC 704 may be anysuitable DAC having any suitable sampling frequency, as the variousaspects described herein implementing a DAC are not limited to use ofany particular type of DAC.

The signal transmit chain 700 b illustrates an example of theamplification stage 705 in which the amplification stage includesfilters 706 and 712, amplifiers 708, 710, and 714, and an optionalimpedance matching network (IMN) 716. The order of componentsillustrated in FIG. 7B illustrates a non-limiting configuration of asignal transmit chain as may be used in systems of the types describedherein.

The filters 706 and 712 and amplifiers 708, 710, and 714 may be anysuitable filters and amplifiers. The amplifiers 708, 710 and 714 may belinear amplifiers, and multiple amplifiers 708, 710, and 714 may beincluded to provide a desired amplification level recognizing that inpractice each amplifier alone may not be able to provide the desiredlevel of amplification. The filters 706 and 712 may be low pass filtershaving cutoff frequencies sufficient to pass the desired signals.Additionally or alternatively, filters 706 and 712 may filter out signalcomponents such as harmonics and/or other spurious signal components.

The impedance matching network 716 may be any suitable active or passiveimpedance matching network for providing desired impedance matchingbetween the array 402 a and the signal transmit chain. In someembodiments, the array 402 a is used to transmit wideband signals oflong duration (i.e., not impulses). In such embodiments, the impedancematching network 716 may be configured to provide wideband impedancematching. In some embodiments, the impedance matching network 716 may beselected to provide a low quality factor (Q) impedance match.

FIG. 7C illustrates an alternative signal transmit chain 700 c to thatof FIG. 7B, and in accordance with the general architecture of FIG. 7A.As shown, the waveform generator of the signal transmit chain 700 c maycomprise or consist of a voltage controlled oscillator (VCO) 703 havingany suitable oscillation frequency. For example, the VCO 703 may beconfigured to generate oscillating signals (e.g., sinusoidal signals)having any of the frequencies described above, or any other suitablefrequencies. The output of the VCO 703 may be provided to theamplification stage 705, which may take the form of previously-describedsignal chain 700 b. However, it should also be appreciated thatalternatives configurations are also possible.

FIG. 9 illustrates a non-limiting example of a signal receive chain(also referred to as a receiver) as may be implemented by systemsaccording to one or more aspects of the present application (e.g., thesystems of FIGS. 2 and 4-6 or any other suitable systems). For example,the illustrated signal receive chain may represent the receiver 412 ofFIGS. 4 and 6, though the receiver 412 may take alternative forms inother embodiments. The signal chain may be linear in some embodiments.

As shown, the signal receive chain 900 of FIG. 9 comprises anamplification stage 902 (e.g., coupled to the array 402 b) andconfigured to receive signals detected by the ultrasound elements of thearray 402 b configured as sensors. The signal receive chain 900 furthercomprises a post-amplification stage 904 which may take various forms,non-limiting examples of which are illustrated in FIGS. 11A-11D anddescribed below.

The amplification stage 902 may be any suitable amplification stage andmay comprise any suitable circuitry for amplifying signals received bythe elements of the array 402 b. The amplification stage 902 may alsoperform additional functions, such as filtering the received signals.According to a non-limiting embodiment, the amplification stage 902includes only a single amplifier and/or filter. Alternatively, theamplification stage 902 may include multiple amplifiers and/or filters.A non-limiting example is illustrated in FIG. 10.

As shown in FIG. 10, the amplification stage 902 may include multipleamplifiers 1004 and 1008. The amplifiers 1004 and 1008 may be anysuitable types of amplifiers, and one or both may be a linear amplifier.The amplifier 1004 may be a variable gain amplifier in the non-limitingembodiment illustrated.

The amplification stage 902 may also include filters 1002, 1006, and1010, which may be any suitable filters. For example, any one of thefilters 1002, 1006, and 1010 may be a low pass filter or a high passfilter having any suitable cutoff frequency to pass the signals ofinterest. In some non-limiting embodiments, one of the filters 1002,1006, and 1010 may be a high pass filter to separate out signals usedfor imaging from signals used for HIFU. As another example, any offilters 1002, 1006, and 1010 may be a notch filter or any other suitabletype of filter for filtering out unwanted narrowband or other signalcomponents, respectively.

The ordering of components illustrated in FIG. 10 is non-limiting, andit should be appreciated that various alternative orderings may beimplemented. Also, it should be appreciated from the foregoingdescription of signal transmit chains and signal receive chains thatboth types of signal chains may be linear according to one or moreembodiments of the present application.

FIGS. 11A-11D illustrate non-limiting examples of the post-amplificationstage 904 of signal receive chain 900. FIG. 11A illustrates analternative in which the signal receive chain 1100 a is configured sothat the output of the amplification stage 902 is provided directly tothe ADC 1106. The ADC 1106 then provides a digital output signal 1110.The output signal 1110 represents a raw received waveform, in thisnon-limiting embodiment. The waveform may be analyzed to determinecharacteristics of interest such as amplitude, phase, and/or frequency,which may be used to determine properties of interest of a subject suchas index of refraction, speed of sound in the subject, attenuation inthe subject, density, and/or other properties.

FIG. 11B illustrates another embodiment of a signal receive chain 1100b, providing a further alternative for the post-amplification stage 904.The signal receive chain 1100 b comprises analog pulse compression stage1116 coupled to the amplification stage 902 and configured to receive anoutput signal from the amplification stage 902. The analog pulsecompression stage 1116 provides an output signal 1118. The analog pulsecompression stage 1116 may apply a pulse compression filter to thereceived signal. To this end, in some embodiments, the received signalmay be correlated with the transmitted signal to produce a correlatedsignal. The correlated signal may be digitized by an analog to digitalconverter to produce output signal 1118.

FIG. 11C illustrates another embodiment of a signal receive chainproviding a further alternative for the post-amplification stage 904. Inthe signal receive chain 1100 c, the output of the amplification stage902 is provided to a detector 1112. In some embodiments, detector 1112may be a square law detector, a logarithmic amplifier detector, a lineardetector, a phase detector, a frequency detector, or any other suitablesignal detector, as aspects of the present application are not limitedin this respect. In some embodiments, the detector may be used toidentify the location of a peak of the received signal, which, may beprovided as output signal 1114. The output signal, in turn, may be usedto obtain one or more measurements of the subject being imaged (e.g.,attenuation measurements).

FIG. 11D illustrates yet another alternative embodiment of a signalreceive chain including a post-amplification stage 904. According to thenon-limiting embodiment of FIG. 11D, the signal receive chain 1100 dincludes a post-amplification stage comprising circuitry configured toperform a heterodyning-type function. The post-amplification stagecomprises circuitry including a mixer 1102, a filter 1104 and theanalog-to-digital converter (ADC) 1106.

The mixer 1102 obtains a reference signal as well as an output signal ofthe amplification stage 902, and combines the output signal with thereference signal to produce a combined signal. The reference signal maybe obtained in any suitable way. As one illustrative non-limitingexample, the reference signal may be a transmission signal obtained fromtransmit circuitry of the system (e.g., from transmitter 408 or anyother suitable transmitter). As another illustrative non-limitingexample, the reference signal may be generated by processing circuitryin the post-amplification stage (and/or by any other suitable processingcircuitry). The processing circuitry may be configured to generate thereference signal at least in part by using a local oscillator. Thereference signal may be a chirp, a pulse, a pulse train, a sinusoid,and/or any other suitable waveform.

In some embodiments, the mixer 1102 may combine the output signal withthe reference signal by multiplying the signals and may output theproduct of the two received signals to a filter 1104, which may be a lowpass filter or any other suitable filter. The filtered output of thefilter 1104 is provided to the ADC 1106, which produces a digital outputsignal 1108 suitable for further processing. Examples of such furtherprocessing are described further below.

In embodiments where the transmitted waveform is a linear FM waveformhaving a pulse length greater than the time it takes for a signal topropagate from array 402 a to array 402 b, the output signal of the ADC1106 may be a tone representing a frequency difference between thetransmitted signal (e.g., from transmitter 408) and the signal receivedby the ultrasound element of the array 402 b and output by theamplification stage 902. For example, in some embodiments the datareceived by the ADC represents the Fourier transform of the time offlight data. The transmissive component of such data may be the largesttonal contributor. As such, performing a Fourier transform of thereceived data may yield a time-domain signal representing thepulse-compressed data—thus, the transmissive component will likelyrepresent a peak in this signal. Therefore, the time-of-flight (TOF) mayprovide information about the speed of sound in a subject, index ofrefraction in the subject, and/or information about other properties ofthe subject. The amplitude of the tone represented by the output signal1108 may be used to determine attenuation of a signal transmitted froman ultrasound element of the array 402 a, which therefore may provideinformation about attenuation within a subject.

The output signals provided by the signal receive chains of FIGS. 9, 10,and 11A-11D may be further processed in some embodiments, for example bypre-processing circuitry 414 and/or any other suitable processingcircuitry. For example, further processing may be performed to measureamplitude, phase, and/or frequency of a signal, among other potentialsignal characteristics of interest. Such pre-processing may be an endresult in some embodiments, or may lead to further analysis of themeasured values in other embodiments, for example to determineproperties of a subject such as density, speed of sound, and/or index ofrefraction. Furthermore, as previously described (e.g., with respect toFIG. 3), one or more volumetric images may optionally be reconstructedillustrating properties of the subject or any other suitable data ofinterest. The type of processing performed by pre-processing circuitry(e.g., pre-processing circuitry 414) may depend, at least in part, onthe manner of operation of the system and the types of signalstransmitted by the opposed arrays. Thus, a description of modes ofoperation of systems of the type described herein is now provided.

According to an embodiment, signals received by ultrasound elements ofan arrangement of the types described herein may be separated byfrequency (or frequency band) for further processing. As describedpreviously, the ultrasound signals transmitted by an arrangement ofultrasound elements may contain multiple frequencies, for example beingwideband signals. The different frequencies of the transmitted signalmay interact differently with the subject, for example in terms ofattenuation and refraction, among other possible differences. Thus,according to an aspect of the present application, receiving circuitrymay process received signals to determine information with respect tospecific frequencies, for example by separating received widebandsignals into frequency components and analyzing those frequencycomponents. In such cases, suitable circuitry may be provided at anypoint in a signal receive chain (e.g., in the signal receive chains ofFIGS. 11A-11D or at any other suitable location within a system) toseparate out frequencies of interest and separately process thedifferent frequency components of a received signal.

Moreover, in such embodiments, separate images may be generated forseparate frequencies. For example, multiple images of index ofrefraction of a subject may be generated, with each image correspondingto a different frequency (or frequency band). Thus, additional data maybe provided beyond what may be achieved by considering only a singlefrequency (or frequency band).

As previously described, according to some embodiments of the presentapplication, a system may be configured to distinguish or discriminateamong multiple ultrasound signals received by an ultrasound sensor frommultiple ultrasound sources. As also described previously, according tosome embodiments of the present application, a system may be configuredto distinguish or discriminate among multiple ultrasound signalstransmitted from ultrasound elements arranged in at least two dimensionsand received by a single ultrasound element configured as a sensor.Multiple modes of operation of systems of the types described herein maybe employed to achieve such results, including code division multipleaccess (CDMA), time division multiple access (TDMA) modes, frequencydivision multiplexing (FDM) modes, as well as combinations of any of twoor more of these modes. Non-limiting examples are described below.

The use of CDMA according to an aspect of the present application isdescribed in the context of system 400 of FIG. 4, for purposes ofillustration. It should be appreciated that CDMA may similarly beemployed in systems of other types described herein as well.

According to an embodiment in which CDMA is implemented by the system400, the ultrasound elements of the array 402 a configured as sourcesmay transmit distinct ultrasound signals concurrently or substantiallysimultaneously. The distinct ultrasound signals may be obtained by usingone or more codes to encode a waveform. For example, in someembodiments, a waveform to be transmitted by multiple ultrasound sources(e.g., a wideband waveform such as a chirp) may be coded, prior to beingtransmitted by an ultrasound source, by using a code associated withthat ultrasound source. As such, multiple ultrasound sources maytransmit distinct waveforms obtained by coding the same underlyingwaveform by using CDMA codes corresponding to the ultrasound sources.

A waveform may be coded by using a CDMA code in any of numerous ways. Insome non-limiting embodiments, an underlying waveform (or a sequence ofwaveforms) may be coded using a so-called intrinsic CDMA coding schemein which the CDMA code may be used to modulate the underlying waveformdirectly (e.g., by computing an exclusive-or between the CDMA code andthe waveform) to produce a coded waveform. The coded waveform may thenbe transmitted. Alternatively, an underlying waveform may be coded usinga so-called extrinsic CDMA coding scheme in which the CDMA code may beused to modulate a waveform indirectly. In this case, the codedwaveform, for a particular ultrasound source, may be obtained bysequentially joining multiple copies of the underlying waveform, witheach copy being phase modulated in accordance with the CDMA codecorresponding to that ultrasound source. Since the phase modulation ofthe set of copies of the underlying waveform depends on the CDMA codecorresponding to the ultrasound source to transmit the coded waveform,distinct coded waveforms will be obtained for each of the ultrasoundsources. These waveforms may then be transmitted. It should beappreciated that the number of copies of the underlying waveform dependson the length of the CDMA code. For example, if a binary CDMA code oflength 10 is used (e.g., to distinguish among 2̂10=1024 ultrasoundsources), the coded waveform may comprise 1024 phase modulated copies ofthe underlying waveform.

Non-limiting examples of suitable CDMA codes include Hadamard codes,Walsh functions, Golay codes, pseudo-random codes (e.g., LML codes) andpoly-phase sequences, among others.

The ultrasound elements of array 402 b configured as sensors may beactive substantially simultaneously, and thus may receive the ultrasoundsignals transmitted by the ultrasound elements of the array 402 a. Thefront-end circuitry such as receiver 412 and/or pre-processing circuitry414 may distinguish (or discriminate between), for each of theultrasound elements of the array 402 b, each of the received ultrasoundsignals from each of the ultrasound elements of the array 402 a bydecoding the signals (e.g., using matched filtering, or in any othersuitable manner). In this manner, a large number of distinctmeasurements (e.g., on the order of N⁴ in some embodiments, aspreviously explained with respect to FIG. 1A) may be made by the systemin a relatively short time period since all the ultrasound signals aretransmitted concurrently or substantially simultaneously.

While the use of CDMA according to an embodiment of the presentapplication may involve transmitting respective coded signals from eachultrasound element of the array 402 a and receiving each of therespective coded signals with each of the ultrasound elements of thearray 402 b, it should be appreciated that alternative implementationsof CDMA according to one or more aspects of the present application arealso possible. For example, in some embodiments distinctly coded signalsmay be concurrently transmitted by two or more ultrasound elements ofthe array 402 a configured as sources and arranged in one or moredimensions. In some embodiments, distinctly coded signals may beconcurrently transmitted by three or more ultrasound elements of thearray 402 a configured as sources and arranged in at least twodimensions. The ultrasound elements of array 402 b configured as sensorsmay receive the distinctly coded signals, which may be decoded andprocessed in any suitable manner (e.g., to form a volumetric image).FIG. 12 illustrates a non-limiting process flow of such operation.

As shown, the method 1200 comprises generating three or more distinctlycoded signals at 1202. The coded signals may be generated in anysuitable manner, for example using a waveform generator (e.g., waveformgenerator 702).

The distinctly coded signals may then be transmitted from three or morerespective elements of an array of ultrasound elements at 1204, such asarray 402 a as a non-limiting example. The three or more respectiveelements may be arranged in at least two dimensions. For example,referring to FIG. 1A, three or more distinctly coded signals may betransmitted from ultrasound elements 110, 112, and 114, respectively.The distinctly coded signals may be transmitted concurrently oraccording to any other suitable timing.

At 1206, the three or more distinctly coded signals may be received byan element of an array (e.g., array 402 b) configured as a sensor. As anon-limiting example, the element 108 of array 102 b in FIG. 1A mayreceive the distinctly coded signals sent from elements 110, 112, and114 of array 102 a. Thus, it should be appreciated that the elementreceiving the three or more distinctly coded signals may, in thisnon-limiting embodiment, receive three or more distinctly coded signalssourced (or transmitted) by ultrasound elements arranged in at least twodimensions. In some embodiments, multiple elements of an array (e.g.,array 402 b) configured as sensors may receive, concurrently, distinctlycoded signals sourced by elements of an array arranged in at least twodimensions.

At 1208, the received signals may be decoded in any suitable manner Forexample, as will be described further below, matched filteringtechniques may be applied to decode the received signals. According to anon-limiting embodiment, each element of an array of ultrasound elementsconfigured as sensors may have a number of decoders associatedtherewith. The number of decoders may, in an embodiment, equal a numberof potential codes to be used in transmitting signals to the elements ofthe array. For example, if 1,024 distinct codes may potentially be usedfor transmitting signals, the element configured as a sensor may have1,024 decoders (e.g., implementing matched filtering) associatedtherewith. It should be appreciated that any suitable number of codesmay be used and therefore any suitable number of decoders may beimplemented on the receiving end of the system.

In some embodiments, where extrinsic CDMA coding may be used to encodethe signals, the signals may be decoded at least in part by averagingcombinations of the received signals. Advantageously, such averaging mayimprove the SNR of the received signals. An example of such operation isnow described.

In some embodiments in which extrinsic CDMA coding is used, eachextrinsically coded signal that is received is multiplied by multiplyingeach pulse of the received signal by the corresponding phase factor forthe transmitter/source being decoded. Then, the resulting multipliedsignal is added into an accumulator for each successive pulse of thereceived signal. Many such multiply-accumulate circuits can operate inparallel to decode multiple transmitters from a single receiver. Theresult, after accumulation, may be an averaged signal for the desiredtransmitter, which, ignoring possible distortions, will have an improvedSNR due to averaging. However, other manners of performing CDMA withextrinsically coded signals are possible.

At 1210, one or more signal characteristics of the received and decodedsignals may be determined. For example, as described previously,characteristics of interest may include amplitude, phase, and/orfrequency, as non-limiting examples.

Further processing may be performed as desired for a given use of thedata determined from 1210. For example, at 1212, one or more volumetricimages may be reconstructed. Alternatively, the method may end withdetermination of the signal characteristics at 1210.

It should be appreciated that the method 1200 of FIG. 12 is anon-limiting example, and that alternatives are possible. For example,one or more processing steps of the received signals may be performedprior to decoding at 1208, such as amplifying, filtering, digitizing,smoothing, and/or any other processing. Any suitable form of linearprocessing may be performed, as the various aspects described herein arenot limited in this respect. A non-limiting example is illustrated inFIG. 13.

As shown, the method 1300 expands upon the method 1200 of FIG. 12 by theinclusion of a pulse-compression step 1302, in which a pulse compressionfilter may be applied. As previously described, in some embodiments,where pulse compression is used, the received signals may be processedby applying a pulse compression filter to the received signals. Applyingthe pulse compression filter may comprise correlating the receivedsignals with a copy of the transmitted signals—a form of matchedfiltering. For example, in some embodiments, where pulse compression isused one or more ultrasound sources may transmit a chirp. The receivedchirp may be correlated with the transmitted chirp. The correlation maybe performed in the time domain or in the frequency domain, as aspectsof the present application are not limited in this respect. Thecorrelation may be performed by any suitable circuitry, including aprocessor, one or more parallel field-programmable gate arrays (FPGA),and/or any other suitable circuitry.

Although not shown, further optional processing may additionally beperformed in the method 1300. For example, decimation of the signalsreceived at 1206 may be performed prior to the pulse compression step1302 or at any other suitable time. Decimation may comprise a low-passfilter operation and down-sampling the received signals to a Nyquistfrequency, for example, to minimize the number of computations performedwith subsequent processing. Furthermore, a complex analytictransformation (e.g., a Hilbert transform) may be applied to thereceived signal to obtain the magnitude information of the receivedsignal (e.g., envelope of the signal) and/or the phase information ofthe received signal. The complex analytic transformation may beperformed after the pulse compression at 1302 and prior to decoding thereceived signals at 1208, according to a non-limiting embodiment.

FIG. 14 illustrates a non-limiting example of processing which may beused to determine one or more signal characteristics at 1210. As shown,determination of one or more signal characteristics may compriseperforming peak arrival detection at 1402 and attenuation detection at1404, as non-limiting examples. Detection of a signal peak itself (“peakdetection”) may be performed together with attenuation detection, or maybe performed as a separate step in some non-limiting embodiments. Theorder of processing need not be the same as that illustrated, as, forexample, the order may be reversed from that shown in FIG. 14.

In some embodiments, peak detection may be performed at least in part byidentifying a portion of the received signal that may contain at leastone peak. The process of identifying a portion of the signal that maycontain the peak is referred to as a “peak arrival detection” process.Peak arrival detection may be performed using any of various suitablemethods. As one non-limiting example, peak arrival detection may beperformed by using a statistical model to detect a change incharacteristics of the received signal. One non-limiting example of sucha model is any model in the family of so-called autoregressive models,which includes, but is not limited to, autoregressive models,noise-compensated autoregressive models, lattice models, autoregressivemoving average models, etc. Accordingly, in some embodiments, peakarrival detection may be performed by fitting a model in the family ofautoregressive models to at least a portion of the received signal. Thismay be done in any suitable way and, for example, may be done by usingleast-squares techniques such as the Yule-Walker algorithm, Burgalgorithm, covariance method, correlation method, etc. An informationcriterion (e.g., Akaike information criterion) may be used to selectmodel order. Though, it should be appreciated that any other statisticalmodel may be used to detect a change in characteristics of the receivedsignal, as aspects of the present application are not limited in thisrespect. Further, any other techniques may be used such as techniquesbased on detecting a percentage of a maximum value. Again, othertechniques may also suitably be used, as these represent non-limitingexamples.

In some embodiments, after the portion of a received signal containing apeak is identified using a peak arrival detection step, the location ofa peak may be identified using any suitable peak detection technique.Non-limiting examples of suitable peak detection methods includetechniques based on group delay processing, sinc interpolation,parabolic processing, detecting a maximum value, and/or cubicinterpolation, among others. Though, it should be appreciated that, insome embodiments, the location of a peak may be identified without apeak arrival detection step. For example, any of the above-identifiedpeak detection methods may be applied directly to the received signal.

Any suitable techniques for performing attenuation detection may beimplemented. In some embodiments, an amount of attenuation may bedetermined by using one or more amplitudes of the received signal andone or more reference amplitudes. The amount of attenuation may bedetermined by computing a ratio (or a log of the ratio) between theamplitude(s) of the received signal and the reference amplitude(s) andcomparing the obtained ratio (or a logarithm of the ratio) with athreshold. An amplitude of the received signal may be an amplitude ofthe received signal at a specific location, such as at a location of apeak (i.e., the amplitude of the peak). An amplitude of the receivedsignal may be an average absolute amplitude computed for a set oflocations, such as over a portion of a signal corresponding to a pulse(e.g., the portion identified by a peak arrival detection technique orany other suitable portion). The reference amplitude(s) may be computedfrom a reference signal in a same manner as amplitude(s) of the receivedsignal are computed. The reference signal may be the transmitted signalor, in some embodiments, may be a reference signal obtained bytransmitting a signal from an ultrasound source to an ultrasound sensorwhen the imaging device is not imaging a subject. Though, it should beappreciated that an amount of attenuation may be determined using othertechniques and, in some embodiments, may be determined by computing aratio of a function of the amplitude(s) of the received signal and afunction of the reference amplitude(s). Any suitable function of theamplitude(s) may be used (e.g., square of the magnitude, cube of themagnitude, logarithm of the magnitude, etc.), as aspects of theinvention described herein are not limited in this respect. In otherembodiments, an amount of attenuation may be determined by using one ormore power values of the received signal and one or more reference powervalues of a reference signal.

The processing illustrated in FIGS. 13 and 14 may be performed by anysuitable computer or hardware. As a non-limiting example, pre-processingcircuitry coupled to a receiver or otherwise configured as part of asignal receive chain may implement one or more of the processesillustrated. A non-limiting example is illustrated in FIG. 15, whichexpands upon the signal receive chain 900 of FIG. 9. As illustrated, thesignal receive chain 1500 comprises, in addition to those components ofthe signal receive chain 900, a pre-processing stage 1502. Thepre-processing stage 1502 in this non-limiting example comprises a firstprocessor 1504, decoders 1506 a, 1506 b, . . . , 1506 n, and a secondprocessor 1508. In this non-limiting example, the first processor 1504may perform operations such as matched filtering, decimation, Hilberttransforms, linear processing and/or any other suitable processing. In anon-limiting embodiment, the processor 1504 may be a digital signalprocessor (DSP). Non-limiting alternatives include one or more FPGAboards, each of which may process signals from one or more signalreceive chains.

The decoders 1506 a-1506 n may decode signals in a CDMA context. Thus,the decoders 1506 a-1506 n may be any suitable type of decoders.Additionally, the number of decoders 1506 a-1506 n may depend on thenumber of potential codes used in transmission of signals within thesystem. For example, as a non-limiting illustration, the number ofdecoders 1506 a-1506 n may correspond to the number of elements (e.g.,of array 402 a) configured to transmit ultrasound signals. As anon-limiting example, if an array of ultrasound elements includes 32ultrasound elements, there may be 32 decoders 1506 a-1506 n.

The decoders 1506 a-1506 n may decode signals and provide their outputsto a second processor 1508, which may perform functions such as thosepreviously described with respect to peak detection, peak arrivaldetection, and/or attenuation detection, among others. The processor1508 may be any suitable type of processor, including a DSP, a pluralityof processing boards, one or more FPGAs, and/or any other suitableprocessor. Also, it should be appreciated that the circuitry ofpre-processing stage 1502 may, in some non-limiting embodiments, beimplemented with a single processor (e.g., a single DSP).

Thus, in view of the foregoing description, it should be appreciatedthat implementing CDMA represents one manner in which a large number ofdistinct signals may be sent and received by a system of the typesdescribed herein in a relatively short time. The use of CDMA maytherefore allow for a large number of measurements of a subject within arelatively short period of time, and may allow for rapid reconstructionof volumetric images of the subject. In some embodiments where CDMAtechniques are implemented, a frame rate of up to 5 frames per second, aframe rate of up to 10 frames per second, a frame rate of up to 25frames per second, a frame rate of up to 50 frames per second, a framerate of up to 75 frames per second, a frame rate of up to 100 frames persecond, a frame rate of up to 125 frames per second may be achieved.

CDMA, however, is not the only manner in which a large number ofdistinct measurements may be made of a subject using systems of the typedescribed herein in a relatively short time. As an alternative or inaddition to CDMA, one or more time division multiple access (TDMA)techniques may be implemented. According to some embodiments of thepresent application, TDMA may be implemented with a system includingopposed arrays of ultrasound elements (e.g., a system of the typeillustrated in FIG. 1A), by activating a single ultrasound elementconfigured as a sensor (or, in other embodiments, multiple ultrasoundelements configured as sensors), and then sequentially transmittingsignals from the ultrasound elements of the apparatus configured assources. A non-limiting example is illustrated with respect to FIG. 16.

As shown, the two arrays 102 a and 102 b are arranged in an opposingconfiguration. At any given time, one or more of the elements of thearray 102 b may be activated and configured as sensors to receivesignals 1602 transmitted from the elements of the array 102 a. Whilethat sensor is activated, a scan of the elements of the array 102 a maybe performed, whereby each of the elements in the scan sequencetransmits one or more waveforms that the activated sensor may beconfigured to receive. Elements 104 of array 102 a may be scanned in anysuitable way. In some embodiments, the elements may be scanned using araster scan pattern, whereby the scan sequence comprises groups ofneighboring elements. FIG. 16 illustrates a non-limiting example ofscanning the elements 104 of the array 102 a using a raster scanpattern, in which the raster scan pattern is illustrated by the dashedarrows. A signal is sent sequentially from each of the elements of thearray 102 a in the non-limiting embodiment shown. However, elements maybe scanned using any suitable scan pattern, as embodiments of theapplication described herein are not limited in this respect. Forexample, in some embodiments, elements may be scanned by using a scanpattern, whereby the scan sequence comprises non-neighboring elements sothat after one element transmits a signal, another element, not adjacentto the first element, transmits the next signal. Such embodiments may beused to keep power deposition levels within specified requirements.

In some embodiments in which TDMA is employed, after an ultrasoundsource has finished transmitting a waveform, there may be a period oftime before any other ultrasound source begins to transmit anotherwaveform. Thus, there may be no ultrasound source transmitting duringthis period of time. The period of time may be any suitable period oftime and may be determined based at least in part on the geometry of thesources and sensors in the imaging device. As an illustrative example,the period of time may be sufficiently long such that a waveformtransmitted from an ultrasound source may be received by an ultrasoundsensor without interference.

The following example may be used as a guide to determining a suitabletemporal spacing of signals in a TDMA context to avoid interference ofthe signals. Assuming for purposes of this example that the volume beingimaged is a medium with minimum speed of sound of c_(min) and maximumspeed of sound c_(max), then for an imaging system with arrays separatedby a distance l and with physical dimensions w and h, the temporal gapΔt between successive pulses to ensure no overlap of the pulses (i.e.,the time between transmission of the tail end of one pulse and the startof the next pulse) is approximatelyΔt>[sqrt(l²+w²+h²)/c_(min)−l/c_(max)]. If the pulse length is given byT, then the period of the pulse train may be T+Δt. Thus, as an example,for an imaging system in which an array of ultrasound sources isseparated from an array of ultrasound sensors by 20 cm, and in whicheach of the arrays has dimensions of 10 cm×10 cm, the temporal gap fortypical tissue speeds (1600 m/s maximum) is about 30 μs. In such anembodiment, it may be preferable to use a temporal gap of approximately50 μs to ensure no overlap of transmitted signals.

It should be appreciated that the formula provided above for determininga suitable time delay Δt is a non-limiting example. For example, a moreconservative approach is to ignore the last term (l/c_(max)) of theabove-noted formula, and instead use Δt>[sqrt(l²+w²+h²)/c_(min)].

In general, when TDMA is employed, the transmitted signals may betransmitted at any suitable times with respect to each other. Asdescribed, one option is to transmit signals sequentially, though notall embodiments are limited in that respect. In such embodiments,signals to be transmitted sequentially may be separated in time byapproximately 1-2 times the time necessary to avoid interference amongsequentially transmitted waveforms. For example, if a transmittedwaveform has a duration of approximately 80 microseconds, a total“window” time allotted to each ultrasound source may be approximately200 microseconds. In other words, the beginning of a waveform sent by afirst ultrasound source may be sent approximately 200 microseconds priorto the beginning of a waveform sent by a second ultrasound source. Othertiming scenarios are also possible, as that described is a non-limitingexample.

In the non-limiting embodiment of FIG. 16, each element 104 of the array102 a may transmit substantially the same signal as the other elementsof the array 102 a. However, due to the sequential nature of thetransmission, a determination may be made upon receipt of the signals(e.g., by suitable front-end circuitry) as to which element of the array102 a transmitted a particular signal, i.e., a received signal may bediscriminated from another received signal. After all the elements ofthe array 102 a have transmitted a signal, a new element of the array102 b may be activated and configured as a sensor to receive signalstransmitted from the array 102 a, while the initially activated elementof array 102 b may be deactivated (e.g., using a demultiplexer or anyother suitable circuitry). Then, another scan of the elements of array102 a may be performed. A non-limiting example of this type of operationis illustrated with respect to the flowchart of FIG. 17A.

As shown, the method 1700 may comprise activating a sensor element at1702. The sensor element may be an element of array 102 b, configured toreceive ultrasound signals transmitted from elements of an array 102 aconfigured as ultrasound sources. At 1704, signals may be transmittedsequentially from three or more elements of an array arranged in atleast two dimensions. The transmitted signals may be received at 1706 bythe activated sensor element. The sensor element may be deactivated at1708 after all the transmitted signals have been detected. At 1710 adecision may be made as to whether the activated sensor element was thelast sensor element. If not, the method may proceed back to 1702, atwhich the next sensor element of the array 102 b may be activated, andthe method may be repeated. After the last sensor element has beendeactivated (i.e., when the answer to the question at 1710 is “yes”),further processing of the received signals may be performed, such as thepreviously described pulse compression at 1302, determination of one ormore signal characteristics at 1210, and reconstruction of one or moreimages of a subject at 1212.

It should be appreciated that FIG. 17A illustrates a non-limitingembodiment, and that variations of the methodology are possible. Forexample, performance of further processing such as application of apulse compression filter, determination of one or more signalcharacteristics, and/or reconstruction of one or more images need notnecessarily wait until the last of the sensor elements has beenactivated and received the transmitted signals. Rather, processing ofreceived signals may occur in parallel to receipt of further transmittedsignals by other activated sensor elements. Other variations on therelative timing of receipt of signals and processing of the signals arealso possible.

Moreover, processing of received signals (e.g., linear processing of thetypes described herein) may be performed by circuitry positioned infront of any demultiplexing circuitry connected to the elements of thereceiving array. For example, a demultiplexer may be coupled to theultrasound elements to provide the time-varying activation of theelements as sensors. However, linear processing circuitry positionedprior to the demultiplexer may perform linear processing on receivedsignals prior to them reaching the demultiplexer. In this manner, theamount of linear processing circuitry may be reduced in someembodiments.

FIG. 17B illustrates an alternative implementation of TDMA according toan embodiment. The illustrated method 1750 may be the preferred mannerof implementing TDMA in some embodiments. The method 1750 differs fromthe method 1700 of FIG. 17A in that, rather than activating a singlesensor element at a time as in the method 1700, multiple sensorselements may be activated simultaneously and thus may receive signalsfrom source elements simultaneously. In a non-limiting embodiment, allsensor elements of an apparatus may be activated simultaneously, thoughnot all implementations of the method 1750 are limited in this respect.

As shown, the method 1750 begins at 1752 with the activation of multiplesensor elements, for example two or more sensor elements. In someembodiments, all sensors elements of an arrangement may be activatedsimultaneously at 1752. A signal may be transmitted from a sourceelement at 1754. The transmitted signal may be received at 1756 by allthe activated sensor elements, i.e., by all the sensor elementsactivated in 1752.

A determination may then be made at 1758 whether the source element fromwhich the signal was transmitted was the last source element to be used.If the answer is “No”, then the method may return to 1754 to transmit asignal from a different source element. In this manner, the method 1750may be iterative, and may implement any suitable number of iterations.

If, however, a determination is made at 1758 that the source elementfrom which the signal was transmitted was the last source element to beused, i.e., if the answer is “Yes”, then the method 1750 may proceed to1302, 1210, and 1212 as shown in FIG. 17B and as previously described inconnection with FIG. 17A.

When the method 1750 follows the iteration path from 1758 back to 1754,any suitable source element may be used upon returning to 1754 totransmit the next signal. In some embodiments, the source element may bea neighboring element to that used during the previous occurrence of1754. In some embodiments, the method may loop back to reactivate thefirst source element of the arrangement of elements, for example, aftera complete scan has been performed. Alternatively, as previousdescribed, any suitable subset of source elements of an arrangement ofelements may be activated in any desired order as part of a scanpattern. Thus, when the method loops back from 1758 to 1754, anysuitable source element may be used to transmit the subsequent signal.

As with the method 1700 of FIG. 17A, it should be appreciated that themethod 1750 of FIG. 17B is also non-limiting, and that alternatives arepossible. For example, performance of further processing such asapplication of a pulse compression filter, determination of one or moresignal characteristics, and/or reconstruction of one or more images neednot necessarily wait until the last of the source elements has been usedto transmit a signal and the signal has been received by the activatedsensor elements. Rather, processing of received signals may occur inparallel to receipt of further transmitted signals transmitted bysubsequent source elements. Other variations on the relative timing ofreceipt of signals and processing of the signals are also possible.

As with the previously described CDMA scheme, it should be appreciatedthat according to the present aspect of the application, TDMA may beused suitably to provide distinct measurements of a subject viacommunication between pairs of source elements and sensor elements withmultiple source elements arranged in at least two dimensions, i.e., thesignals received by sensor elements may be discriminated to determinefrom which source element the signals were emitted. Thus, either theCDMA previously described or the TDMA according to the present aspectmay be used to provide volumetric imaging of a subject, according tonon-limiting embodiments.

It should also be appreciated that TDMA may be applied withouttransmitting signals from all elements of an arrangement of elementsconfigured as sources and/or without receiving signals with all elementsof an arrangement of ultrasound elements configured as sensors. Rather,any desired number and arrangement of elements configured as sources maybe used to transmit signals at different times from each other, and anydesired number and arrangement of ultrasound elements configured assensors may be used to receive the transmitted signals. For example, insome embodiments it may be desirable to transmit signals only from asubset of an array of ultrasound elements configured as sources. Use ofonly a subset of sources and/or a subset of sensors may provide higherspeed operation in some embodiments. Thus, the aspects described hereinare not limited to using all sources and sensors of an arrangement ofsources and/or sensors.

Furthermore, according to an aspect of the present application, acombination of CDMA and TDMA techniques may be employed. As anon-limiting example, multiple subsets of ultrasound elements of anarray of ultrasound elements may be sequentially activated (or otherwiseactivated at different times) to transmit ultrasound signals. Theultrasound elements within each subset may transmit distinctly codedsignals, while elements of a subsequently activated subset of elementsconfigured as sources may utilize the same or different codes as thoseutilized by a previously activated subset, but at a different time. Inthis manner, a combination of the benefits achieved via CDMA and TDMAtechniques may be obtained. For example, CDMA techniques may providefaster transmission and collection of data than that of TDMA, forexample, because according to an aspect in which CDMA techniques areemployed, ultrasound signals from multiple elements configured assources may be transmitted concurrently and multiple ultrasound elementsconfigured as sensors may concurrently receive signals. However, thecircuitry and systems utilized to implement CDMA operations may be morecomplex than that of TDMA, for example, because of the complexity ofdecoding involved. By contrast, TDMA may provide relatively sloweroperation than that of CDMA (e.g., lower frame rates), but may providebenefits in terms of simplicity of system design. Implementing acombination of TDMA and CDMA as explained above may allow for achievinga beneficial intersection between speed of operation and complexity ofcircuit design.

It should be appreciated that operation of a system according to TDMAprinciples may be achieved using any suitable circuitry, non-limitingexamples of which have been previously described. For example, signaltransmit chains such as those illustrated in FIGS. 7A-7C may beemployed. Signal receive chains such as those of FIGS. 9, 10, and11A-11D may be employed. The signal receive chain of FIG. 15 may bealtered in a TDMA context, for example, by removal of the decoders 1506a-1506 n. In such a scenario, the pre-processing stage 1502 may compriseat least one processor (e.g., processors 1504 and 1508 may be combined)or any suitable hardware configuration for performing the functionspreviously described absent decoding of the type performed by decoders1506 a-1506 n. Thus, the various aspects in which TDMA techniques areemployed are not limited to the specific circuitry used.

Frequency division multiplexing is a further manner of operation, whichmay be implemented according to an aspect of the present application.Frequency division multiplexing may be implemented in any suitablemanner For example, sources (e.g., of array 102 a) may first transmitsignals in a first band having a first center frequency and subsequentlytransmit signals in a second band having a second center frequency.Alternatively, different subsets of an arrangement of ultrasoundelements may transmit at different bands of frequencies. A band offrequencies may consist of only one frequency or have multiplefrequencies. Thus, those aspects described herein in which frequencydivision techniques are used are not limited to the particular manner inwhich frequency division operation is achieved.

Moreover, frequency division techniques may be employed in combinationwith CDMA and/or TDMA in any suitable manner. As one non-limitingexample, a frequency hopping code division multiple access (FH-CDMA)technique may be used. In some embodiments, orthogonal frequencydivision multiple access (OFDMA) may be implemented, which is atechnique of having different transmitters occupying different sets offrequencies at different times. That is, for one pulse, a singletransmitter (or group of transmitters) may occupy a certain set offrequencies, while another transmitter (or group of transmitters)occupies a different (orthogonal) set of frequencies. The occupiedfrequencies then change on the next pulse according to a predeterminedcode sequence.

Systems and methods of the types described herein may provide for rapidcollection of large amounts of data regarding a volume or 3D subject ofinterest. As also described previously, high resolution volumetricimages may be generated rapidly. Also, in at least some embodiments, thecircuitry implemented by systems of the types described herein may havebeneficial characteristics. For example, the signal chains describedherein may be linear (e.g., a linear signal transmit chain and/or linearsignal receive chain), which may allow for rapid and efficient signalprocessing and robust operation. Other benefits may also be achieved.

Reconstructed images, such as those produced as part of the methods ofFIGS. 12, 13, 17A and 17B may be used for any suitable purpose(s),examples of which are described. In some embodiments, one or more images(e.g., one or more volumetric images) of a subject may be used toclassify the subject or a portion of the subject. For example, imagedsubjects may be classified as a type of tissue, a type of organ (e.g.,kidney, liver, etc.), or may be classified according to any desiredclasses. Classification, when performed, may be based on detected shapein some embodiments (e.g., by looking at coefficients of sphericalnorms, shape metrics, shape descriptors (e.g., spherical harmonics), orany features characterizing shape, as examples). In some embodiments,classification may be performed based on collected data values (e.g.,time-of-flight values, attenuation values, speed-of-sound values,dispersion coefficients, etc.). In some embodiments, classification maybe based on changes in (e.g., gradients) these types of data values.Other manners of classification are also possible.

Various aspects of the present application have been described withrespect to opposed arrays of ultrasound elements. However, it should beappreciated that various aspects of the present application are notlimited to use with opposed arrays of ultrasound elements. Rather,various alterations are possible. Several are now described.

As has been explained, for example, with respect to FIG. 1A, one or moreaspects of the present application may apply to systems includingopposed arrangements of ultrasound elements forming arrays. However,arrays represent a non-limiting configuration. For instance, theultrasound elements need not be arranged in an array of evenly (oruniformly) spaced elements, but rather may assume practically anyarrangement in which the elements are arranged in at least twodimensions. A first non-limiting alternative example is illustrated inFIG. 18A, in which the ultrasound elements of a single arrangement arearranged irregularly, i.e., not all the ultrasound elements are spacedat regular (uniform in some embodiments) intervals with respect toneighboring ultrasound elements. As shown, the arrangement 1800 ofultrasound elements 1802 includes, among others, ultrasound elements1802 a-1802 i. Uniformly spaced dashed grid lines are also illustrated.As shown, ultrasound element 1802 e is not spaced at a regular distancefrom its neighboring ultrasound elements 1802 a-1802 d and 1802 f-1802i. Rather, in the non-limiting embodiment illustrated, ultrasoundelement 1802 e is disposed more closely to ultrasound elements 1802 b,1802 c, and 1802 f than it is, for example, to ultrasound elements 1802d, 1802 g, and 1802 h. As shown, while the other ultrasound elements ofthe illustrated arrangement 1800 are centered on grid lines, ultrasoundelement 1802 e is not. Although the majority of the ultrasound elementsof the arrangement 1800 may be regularly spaced, the displacement ofultrasound element 1802 e from a regular spacing means that thearrangement 1800 is an irregular arrangement.

In some embodiments, positions of elements in an arrangement ofirregularly-spaced elements may be derived from positions ofregularly-arranged points in a higher-dimensional space. The positionsof elements may be derived from the positions of regularly-arrangedpoints by mapping or projecting the positions of the regularly-arrangedpoints to the lower-dimensional space of the arrangement ofirregularly-spaced elements. In some embodiments, for example, thespacing of elements in an arrangement of irregularly-spaced elements maybe obtained at least in part by arranging, regularly, a set of points ona three-dimensional object (e.g. a sphere, a cylinder, an ellipsoid,etc.) and projecting this set of points onto a plane to obtain a set ofpositions for elements in the arrangement of irregularly-spacedelements. A set of points may be regularly arranged on athree-dimensional object in any suitable way. As a non-limiting example,a set of points may be regularly arranged on a sphere by being placedwith uniform spacing along one or more great circles of the sphere, bybeing placed at points of intersection between the sphere and a polygon(e.g., icosahedron), being regularly placed with respect to solid anglesof the sphere, and/or in any other suitable way. Though, it should beappreciated that the set of points is not limited to being regularlyarranged on a three-dimensional object and may be regularly arranged ona higher-dimensional object of any suitable dimension (e.g., ahypersphere of any suitable dimension greater than or equal to three).The set of points may be projected using a stereographic projection, alinear projection, or any other suitable projection technique ortechniques, as aspects of the disclosure provided herein are not limitedin this respect. It should be appreciated that a projection of regularlyarranged points from a higher-dimensional space (e.g., fromthree-dimensional space) to a lower-dimensional space (e.g., a plane)may be irregular.

In some embodiments, an irregular arrangement of ultrasound elements mayconform to a Penrose tiling scheme. In some embodiments, an irregulararrangement of ultrasound elements may exhibit varying spacing ofelements within the arrangement, such as greater spacing of elementstoward the center of the arrangement and closer spacing of elementstoward the edges (perimeter) of the arrangement.

In the non-limiting embodiment of FIG. 18A, only one ultrasound element(i.e., ultrasound element 1802 e) is disposed at an irregular spacingwith respect to the other ultrasound elements of the arrangement.However, it should be appreciated that irregular spacing does notrequire any particular number or percentage of ultrasound elements of anarrangement to be irregularly spaced with respect to the otherultrasound elements. Rather, an arrangement of ultrasound elements maybe irregular if any one or more ultrasound elements of the arrangementare irregularly spaced from neighboring elements. In some embodiments, asubstantial percentage of ultrasound elements of an ultrasound elementarrangement (configured as sources or sensors) may be regularly spacedwith respect to neighboring ultrasound elements. By contrast, in someembodiments a substantial percentage of ultrasound elements of anultrasound element arrangement (configured as sources or sensors) may beirregularly spaced with respect to neighboring ultrasound elements. Insome embodiments, a majority of ultrasound elements of an ultrasoundelement arrangement (configured as sources or sensors) may beirregularly spaced with respect to neighboring ultrasound elements.

FIGS. 18B and 18C illustrate alternative irregular arrangements to thatof FIG. 18A, with each figure including a grid defined by uniformlyspaced grid lines for purposes of illustration. The arrangement 1820 ofFIG. 18B includes ultrasound elements 1802 that are spaced more closelytogether toward the center of the arrangement (i.e., toward element 1802j in the center of the arrangement 1820) and more widely apart towardthe edges of the arrangement. Thus, as shown, the spacing betweenneighboring ultrasound elements of the arrangement 1820 increases movingoutwardly from the center of the arrangement.

FIG. 18C illustrates an irregular arrangement 1830 of ultrasoundelements 1802 that are spaced more closely together toward the edges ofthe arrangement and more widely apart toward the center of thearrangement (i.e., toward ultrasound element 1802 j).

According to an embodiment of the present application, arrangements ofultrasound elements used in combination, for example for transmissiveultrasound imaging, may be irregular and need not have identicallayouts. FIG. 18D illustrates a non-limiting example. The system 1840includes a first paddle 1842 a and a second paddle 1842 b, eachincluding a respective support 1844 a and 1844 b and a respective handle1845 a and 1845 b. Each of the paddles also includes a respectivearrangement 1846 a and 1846 b of ultrasound elements. The arrangementsmay be configured to operate in combination in a transmissive ultrasoundimaging modality. Yet, as shown, each of the two arrangements isirregular and they are not irregular in the same manner, i.e., thearrangements do not exhibit identical element layout to each other. Asillustrated, the two arrangements 1846 a and 1846 b also have differentnumbers of ultrasound elements than each other. Even so, using one ormore of the operating techniques described herein, the arrangements 1846a and 1846 b may be used in combination for ultrasound imaging (e.g.,with the arrangement 1846 a including ultrasound elements configured asultrasound sources and the arrangement 1846 b including ultrasoundelements configured as ultrasound sensors) or other suitable purposes.

A further potential alternative to use of arrays of ultrasound elementsis to use a random arrangement of ultrasound elements. As used herein, arandom arrangement is one in which there is no generally discernibleregular spacing between elements of the arrangement, irrespective ofwhether the elements are arranged in a mathematically random mannerThus, a random arrangement, as that term is used herein, represents oneexample of an irregular arrangement, but not all irregular arrangementsare random arrangements.

Moreover, it should be appreciated that an irregular (e.g., random)arrangement of ultrasound elements may be effectively created byoperating only a subset of ultrasound elements of an arrangement,wherein the subset of elements constitutes a random arrangement evenwhile the overall arrangement may not constitute a random arrangement.

A non-limiting example of a random arrangement of ultrasound elements isillustrated in FIG. 19 as arrangement 1900. As shown, there is nogenerally discernible regular spacing between the ultrasound elements1902 of the arrangement 1900. As with the foregoing explanation of anirregular arrangement, according to an aspect of the present applicationsimply knowing the relative positions of the ultrasound elements 1902may be sufficient to allow for suitable discriminate and processing ofdata collected by the arrangement.

The irregular and random arrangements of FIGS. 18A-18D and 19 mayprovide one or more benefits. For example, the ability to use sucharrangements of ultrasound elements while collecting 3D data may relaxdesign constraints and manufacturing tolerances with respect toconstruction of the arrangements of ultrasound elements (and thereforethe devices in which such arrangements may be embodied). As anotherexample, the irregular spacing of ultrasound sources and/or sensors maylead to fewer artifacts in images calculated from measurements obtainedby using ultrasound sources/sensors so spaced. The irregular spacing maylead to fewer artifacts that ordinarily result from symmetry in regularsensor arrangements.

As will be described further below, it may desirable to know therelative positions of ultrasound elements of an arrangement, forexample, in interpreting data collected by the arrangement and producingimages. Utilizing an arrangement of ultrasound elements regularly spaced(e.g., an array as in FIG. 1A) may simplify analysis of data collectedby the arrangement, but is not a necessity in all aspects of the presentapplication. Rather, as will be described further below, knowing therelative positions of ultrasound elements of an arrangement, whether ornot those positions represent a regular spacing, may be sufficient toallow for suitable discrimination and analysis of data collected by thearrangement. Thus, knowing the relative positions of ultrasound elementsof irregular arrangements such as those of FIGS. 18A-18D may besufficient in some embodiments to allow for suitable discrimination andanalysis of data collected by such arrangements for imaging or otherpurposes.

According to an aspect of the present application, an arrangement ofultrasound elements in two or more dimensions may be a sparsearrangement. Sparsity, in this context, may relate to a wavelength ofsignals transmitted between pairs of ultrasound elements arranged assources and sensors. In some embodiments, sparsity of an arrangement,whether an arrangement of sources or sensors, may be defined withrespect to a wavelength of radiation as transmitted by sources. However,in some cases, sparsity may be defined with respect a receivedwavelength. As previously described, signals transmitted by ultrasoundelements configured as sources may have a given frequency or, in thecase of broadband signals, may have a center frequency. The frequency,or center frequency as the case may be, has a corresponding wavelengthλ. The arrangement of ultrasound elements may be sparse in that λ/2 maybe smaller than the spacing between neighboring ultrasound elements ofthe arrangement. For example, as shown in the non-limiting embodiment ofFIG. 20, which illustrates a single arrangement 2000 of ultrasoundelements 2002, the ultrasound elements of a row of the arrangement maybe spaced from each other by a distance p, such that the distance 2p maybe greater than λ of the transmitted or received signals operated on bythe arrangement 2000 (stated another way, p>λ/2). In some embodiments,the distance p may be greater than ¾λ, greater than λ, greater than 2λ,greater than 3λ, or take any other suitable value greater than λ/2.Despite the sparse spacing of ultrasound elements of the arrangement2000, accurate collection of data providing sufficient resolution of asubject may be provided by using the techniques described further belowwith respect to volumetric image construction.

It should be appreciated that a sparse arrangement as that term is usedherein need not require the distance between every pair of neighboringultrasound elements of the arrangement to be greater than λ/2. Rather, asubset of ultrasound elements may be separated from their respectivenearest neighbors by a distance p greater than λ/2. In some embodiments,a sparse arrangement may be formed with respect to active elements of anarrangement (e.g., active sources and/or active sensors), even if thearrangement includes additional elements. A sparse arrangement does notrequire uniform pitch of ultrasound elements, but rather may have anon-uniform pitch. According to an embodiment, a sparse arrangement mayhave a non-uniform pitch and may be characterized by a minimum pitch ofthe arrangement that is greater than λ/2. In some embodiments, more thanapproximately 95% of the elements have a spacing greater than λ/2, ormore than approximately 90%, more than approximately 80%, more thanapproximately 70%, more than approximately 60%, more than approximately50%, or more than approximately 40% have a spacing greater than λ/2.

As will be described further below, one or more benefits may be achievedusing sparse arrangements of the types described above in connectionwith FIG. 20. For example, the ability to use a sparse arrangement ofultrasound elements may allow for a reduction in the total number ofultrasound elements needed to achieve particular imaging performancecriteria, such as resolution. Thus, cost and design of an ultrasoundarrangement may be reduced. In addition, as will be described furtherbelow, the ability to use the sparse arrangement of ultrasound elementsmay allow for provision of additional elements of a different type orserving a different purpose to be positioned among the ultrasoundelements configured to operate as sources and sensors in an imagingmodality. For example, use of a sparse arrangement of ultrasoundelements configured to operate in an imaging modality may facilitateplacement of high intensity focused ultrasound (HIFU) elements among theelements configured for imaging. Thus, use of a sparse arrangement ofultrasound elements configured to operate in an imaging modality mayfacilitate use of a collection of ultrasound elements as a dual- ormulti-mode device.

The above-described embodiments relating to irregular and sparse arraysmay be used in combination in one or more embodiments. In someembodiments, an arrangement of ultrasound elements may be both sparseand irregular, though alternatives are possible. For example, anarrangement of ultrasound elements may be a sparse arrangement but mayalso exhibit regular spacing of all the ultrasound elements from theirneighbors. In a further embodiments, an arrangement of ultrasoundelements may be irregular but not sparse. In some embodiments, anarrangement may be neither sparse nor irregular.

As a further alternative to those embodiments illustrated thus far, itshould be appreciated that ultrasound elements of an arrangement may bearranged in three dimensions. While FIG. 1A, among others, hasillustrated substantially planar arrangements of ultrasound elements,the various aspects of the present application are not limited in thisrespect. Referring to FIG. 21, an arrangement 2100 of ultrasoundelements 2102 is illustrated. As shown, the ultrasound elements 2102 arearranged along three dimensions, not just two, assuming differentpositions in the x, y, and z-axes. Some of the ultrasound elements areseparated along the z-axis by a distance Δz, which may have any suitablevalue, ranging from, for example, a few millimeters to a several inchesor more. The illustrated arrangement 2100 may represent a firstarrangement of ultrasound elements, and according to some embodiments asecond arrangement of ultrasound elements may be provided which mayoperate in connection with the illustrated arrangement. For example, asecond arrangement of ultrasound elements may be disposed in asubstantially opposed position with respect to the arrangement 2100 ofFIG. 21. The first arrangement may operate as a collection of ultrasoundsources, while the second arrangement (not shown) may operate as acollection of ultrasound sensors, as a non-limiting example. Thus,according to a non-limiting embodiment, substantially opposedthree-dimensional arrangements of ultrasound elements may be provided.

Furthermore, in those embodiments in which three-dimensionalarrangements of ultrasound elements are provided, it should beappreciated that the arrangements may take any suitable form and theelements may have any suitable spacing therebetween. For example, thearrangements of ultrasound elements in three dimensions may be regulararrangements, irregular arrangements, and/or sparse arrangements, amongothers.

FIG. 22A illustrates a non-limiting example of an arrangement ofultrasound elements configured as sources and sensors, and which may besuitable for receiving a subject for imaging of the subject. As shown,the system 2200 includes a substantially cube-shaped (or box shaped)arrangement of ultrasound elements. In particular, in the non-limitingembodiment shown, the system 2200 includes ultrasound elementsconfigured as sides 2202 a-2202 d of a cubic structure, with suchultrasound elements being configured as ultrasound sources. In thenon-limiting embodiment shown, 2202 d may represent the bottom of thecubic structure, but may generally be referred to as a side. The system2200 further comprises ultrasound elements arranged on a side 2204 andconfigured to operate as ultrasound sensors. The cubic structureillustrated may have an open top, such that a subject 2206 may beinserted into the volume between the ultrasound elements configured assources and those configured as sensors. The subject may be any type ofsubject, such as a medical patient (e.g., breast, a head, a hand, or anyother suitable portion of a patient) or other subject of interest. Itshould be appreciated that use of a configuration such as that shown inFIG. 22A may allow for volumetric imaging of the subject 2206, forexample, because ultrasound signals may be sourced from multiple angleswith respect to the subject 2206.

In the configuration of FIG. 22A, the sides 2202 a-2202 d may beconsidered distinct arrangements of ultrasound elements, such that thenon-limiting embodiment illustrated includes four distinct arrangementsof ultrasound elements configured as ultrasound sources. More generally,embodiments of the present application provide for two or more distinctarrangements of ultrasound elements configured as sources, with someembodiments consisting of two distinct arrays of ultrasound elementsconfigured as sources. The two or more distinct arrangements, incombination with one or more arrangements of ultrasound elementsconfigured as sensors may substantially surround a subject. According toa non-limiting embodiment involving the configuration of FIG. 22A, oneor more of the ultrasound elements of side 2204 configured to operate asultrasound sensors may receive respective signals from at least oneultrasound element of any two or more of the sides 2202 a-2202 d (and insome cases from all of the sides 2202 a-2202 d). Such signals may bediscriminated in any suitable manner, such as any of those describedelsewhere herein.

FIG. 22B illustrates an alternative arrangement to that of FIG. 22A. Asshown, the system 2250 includes ultrasound elements 2252 configured asultrasound sources and indicated by boxes, together with ultrasoundelements 2254 configured as ultrasound sensors and indicated by circles.The ultrasound elements 2252 and 2254 may be disposed in a substantiallyhelical pattern (or other cylindrical configuration), as shown. In someembodiments, the ultrasound elements 2252 and/or 2254 may be configuredon a support 2256, which may accommodate insertion of the subject 2206for imaging or other investigation. In some embodiments, an arrangementof ultrasound elements like that shown in FIG. 22B may be a sparsearrangement and/or an irregular arrangement. The helical pattern maycomprise one or multiple helices, as aspects of the disclosure providedherein are not limited in this respect.

FIG. 22C illustrates a variation on the apparatus of FIG. 22A. Namely,FIG. 22C illustrates an apparatus 2260 similar to that of FIG. 22A butwithout the sides 2202 b, 2202 c and 2202 d. The apparatus 2260therefore includes ultrasound elements configured as side 2202 a andultrasound elements arranged on a side 2204 and configured to operate asultrasound sensors. The angle α between sides 2202 a and 2204 may takeany suitable value in this non-limiting embodiment, such as beingbetween zero degrees and forty-five degrees, between ten degrees andsixty degrees, between forty degrees and ninety degrees, or having anyother suitable value. Thus, it should be appreciated that embodiments ofthe present application provide arrangements of ultrasound elementstilted with respect to each other (e.g., tilted by any of the anglespreviously described or by any other suitable angle). In someembodiments, an arrangement of ultrasound elements configured asultrasound sources may be tilted relative to an arrangement ofultrasound elements configured as ultrasound sensors. In someembodiments, an arrangement of ultrasound elements configured asultrasound sources may be tilted relative to another arrangement ofultrasound elements configured as ultrasound sources. In someembodiments, an arrangement of ultrasound elements configured asultrasound sensors may be tilted relative to another arrangement ofultrasound elements configured as ultrasound sensors.

It should be appreciated that the arrangements of ultrasound elementsdescribed herein may take any suitable dimensions. As previouslydescribed, the arrangements may comprise any suitable number ofultrasound elements, for example to provide a desired resolution. Theultrasound elements may be arranged in a manner sufficient to imagesubjects of interest, such as a patient's head, breast, hand, or othersubjects of interest. Thus, arrangements of ultrasound elements asdescribed herein may occupy distances ranging from centimeters up toseveral inches or more. As a non-limiting example, an arrangement ofultrasound elements may be approximately 15 cm×15 cm, less thanapproximately 100 cm×100 cm, or any other suitable size.

Various aspects of the present application have been described in whichone or more ultrasound elements are implemented. It should beappreciated that the various aspects implementing ultrasound elementsare not limited in the type of ultrasound elements used. Any suitabletype of ultrasound elements may be implemented, and in certainapplications the type of ultrasound element used may be selected basedon considerations such as size, power, and material, among others. Forexample, conventional piezoelectric ultrasound elements may be used,and/or capacitive micromachined ultrasound transducers (CMUT) may beused, though other types are also possible. In one embodiment, CMUTelements may be used to form an array of ultrasound elements configuredas sources to transmit ultrasound radiation. CMUT elements may be usedfor both imaging and HIFU functionality, and therefore may simplifydesign of an array of ultrasound elements in some embodiments. In someembodiments, it may be desirable to perform ultrasound imaging incombination with MRI, such that it may be preferred for the ultrasoundelements to be formed of a material suitable for operation in thepresence of strong magnetic fields.

Non-limiting examples of ultrasound elements which may be used in any ofthe embodiments described herein include CMUT, lead zirconate titanate(PZT) elements, lead magnesium niobate-lead titanate (PMN-PT) elements,polyvinylidene difluoride (PVDF) elements, high power (“hard”) ceramicssuch as those designated as PZT-4 ceramics, or any other suitableelements. Materials designated as PZT-8 materials may be preferable foruse as HIFU elements in some embodiments. In some embodiments,ultrasound elements configured as sources may be of a first type whileultrasound elements configured as sensors may be of a second type. Forexample, according to an embodiment, PZT elements may be used to form anarray of ultrasound elements configured as sources, while PVDF elementsmay be used to form an array of ultrasound elements configured assensors. Such a configuration may be implemented for any purpose(s). Insome embodiments, PVDF elements may be more efficient in terms ofreceiving signals, but may be characterized by an undefined outputimpedance. Thus, it may be desirable to couple such PVDF elements tohigh impedance low noise amplifiers (LNAs), which may be best suited forreceipt of ultrasound signals rather than sourcing ultrasound signals.PZT elements, on the other hand, may be better suited in someembodiments to operate as ultrasound sources. Thus, embodiments of thepresent application provide for suitable mixing of radiation elementtypes as sources and sensors to provide desired operation.

It should be appreciated from the foregoing that according to someembodiments of the present application an ultrasound system suitable forperforming volumetric imaging of a subject may be provided in which thearrangements of ultrasound elements do not enclose the subject. Theability to collect volumetric data of a subject without the need toenclose or substantially enclose the subject may facilitate operation ofthe system, for example, by facilitating arrangement of the ultrasoundelements with respect to the subject. Various configurations ofultrasound elements suitable for performing volumetric imaging of asubject without substantially enclosing the subject are possible.

For example, referring to FIG. 1A, it should be appreciated that thearrays 102 a and 102 b of ultrasound elements define a volumetherebetween, and that the arrays do not substantially enclose thevolume. Thus, a subject disposed within the volume will not besubstantially enclosed by the arrays of ultrasound elements. Forexample, there may be no part of the system that forms a closed looparound the subject or even a substantially closed loop.

As a further non-limiting example, reference is made again to FIG. 4 inwhich, similar to FIG. 1A, it should be appreciated that the arrays 402a and 402 b of ultrasound elements define a volume 418 therebetween, butdo not substantially enclose the volume. Thus, the subject 410 is notsubstantially enclosed by the arrays 402 a and 402 b. Nonetheless, evenwith leaving the arrays 402 a and 402 b in static locations, volumetricimaging of the subject 410 may be achieved as described previously.

While FIGS. 1 and 4 illustrate non-limiting examples in whicharrangements of ultrasound sources and sensors do not substantiallyenclose a subject, it should be appreciated that the arrangements neednot be substantially planar. For example, arrangements of ultrasoundelements may be curved while still not substantially enclosing thesubject. For example, arrangements of ultrasound elements may be formedon flexible supports such as those of FIG. 28, and curved to conform toa patient without substantially enclosing the patient. Whether or not anarrangement of ultrasound elements substantially encloses a subject maydepend on the context. In some embodiments, an arrangement does notsubstantially enclose a subject if the arrangement does not form anyclosed contour around the subject (see, e.g., FIGS. 4-6). In someembodiments, an arrangement does not substantially enclose a subject iftwo or more sides of the subject are accessible.

In some embodiments, a system comprising two or more arrangements ofultrasound elements may be said to not substantially enclose a subjectif there is a gap separating the arrangements. In some embodiments, thegap may be at least five inches, at least 10 inches, at least one foot,at least several feet, or more. In some embodiments, the gap may bebetween approximately 6 inches and 18 inches. In some embodiments, thegap may be sufficiently large to allow access to the subject while thesystem is in operation (e.g., to allow a doctor to touch the subject).An arrangement of ultrasound elements may be said to not substantiallyenclose a subject in some embodiments if the subject may be insertedinto and/or removed from the arrangement without needing tosubstantially alter the position of the arrangement. An arrangement ofultrasound elements may be said to not substantially enclose a subjectin some embodiments if there is a substantial solid angle, defined withits vertex corresponding to the subject, which is not occupied bysources or sensors. For example, non-ring shaped arrangements andnon-cylindrical arrangements may be said to not substantially enclose asubject in some embodiments. FIG. 47 illustrates an example, in which anarrangement of radiation elements (e.g., ultrasound elements) 4702 isconfigured to operate in combination with an arrangement of radiationelements (e.g., ultrasound elements) 4704 to image a subject 4709. Asolid angle 4706 defined with respect to the subject (i.e., having itsvertex 4708 located at the position of the subject) is free from anyultrasound elements. The solid angle may assume any suitable valuedepending on the context. For example, the solid angle 4706 may be atleast at least π/5 steradians, at least π/4 steradians, at least π/2steradians, at least it steradians, at least 2π steradians, betweenapproximately π/10 and 3π steradians, between approximately π/5 and 3πsteradians, between approximately π and 3π steradians or any othersuitable non-zero solid angle. In some embodiments, such a configurationof ultrasound elements may be said to not substantially enclose thesubject.

It should also be appreciated from the foregoing description that,according to an aspect of the present application, a system may comprisean arrangement of ultrasound elements configured to operate asultrasound sources, which is separated from an arrangement of ultrasoundelements configured to operate as ultrasound sensors. For example, againreferring to FIG. 1A, it should be appreciated that the array 102 a mayinclude ultrasound elements 104 configured to operate as ultrasoundsources, and that those ultrasound elements are separated in thenon-limiting embodiment illustrated from the ultrasound elements 104 ofarray 102 b arranged to operate as ultrasound sensors. The distance ofseparation is not limiting. For example, referring to FIG. 1A, the array102 a may be separated from the array 102 b by any suitable distance,such as one inch, two inches, between two and six inches, between oneand ten inches, between 1-30 centimeters, between 10-50 centimeters, orany other suitable distance. Furthermore, the distance of separationneed not be the same for all pairs of ultrasound elements of the array102 a with respect to those of the array 102 b. For example, as has beendescribed, arrangements of ultrasound elements that are not strictlyplanar may be implemented according to one or more aspects of thepresent application (see, e.g., FIG. 21), and thus the distances betweenpairs of ultrasound elements configured as sources and those configuredas sensors of an opposing arrangement may not be the same. Also, as willbe described further below, arrangements of ultrasound elements may beformed on curved, flexible, and/or deformable surfaces, such that thedistance between one portion of a first arrangement and a secondarrangement may differ from the distance between a second portion of thefirst arrangement and second arrangement.

Referring to FIG. 23, according to an embodiment of the presentapplication, an arrangement of ultrasound elements configured to operateas ultrasound sources may be separated from an arrangement of ultrasoundelements configured to operate as ultrasound sensors by a plane. Asshown, the plane 2300 may separate the array 102 a of ultrasoundelements from the array 102 b of ultrasound elements. In someembodiments, all of the ultrasound elements configured to operate asultrasound sources may be on one side of the plane 2300, while all theultrasound elements configured to operate as sensors may be on theopposite side of the plane 2300. In other embodiments, each of arrays102 a and 102 b may include both sensors and sources.

It should be appreciated that the ultrasound elements of an arrangementneed not be limited to performing only one function. For example,referring again to FIG. 23, the ultrasound elements of the array 102 amay be configured to operate for a first period of time as ultrasoundsources, but at a later period of time as ultrasound sensors. Similarly,the ultrasound elements of arrangement 102 b may be configured tooperate at different times as ultrasound sources and sensors. Accordingto an embodiment, arrangements of ultrasound elements disposed in anopposed relationship with respect to each other may be configured toalternate their mode of operation. For example, the ultrasound elementsof array 102 a may be configured to operate as ultrasound sources whilethe ultrasound elements of array 102 b may be configured to operate asultrasound sensors, and then the respective functions of the ultrasoundelements of the two arrays may be alternated over time.

FIG. 24 illustrates another non-limiting example of a manner in whicharrangements of ultrasound elements configured as ultrasound sources maybe separated in space from ultrasound elements configured as ultrasoundsensors. As shown, the system 2400 includes an arrangement of ultrasoundelements 2402 a and a second arrangement of ultrasound elements 2402 b.For purposes of illustration, the ultrasound elements of the arrangement2402 a may be configured to operate as ultrasound sources, whereas theultrasound elements of arrangement 2402 b may be configured to operateas ultrasound sensors. The convex surface (i.e., convex hull (thesmallest convex surface) or any other convex surface) enclosing thearrangement 2402 a is identified by 2404 a. Similarly, the smallestconvex hull enclosing the arrangement 2402 b of ultrasound elements isidentified by 2404 b. As seen, the convex hull 2404 a does not intersectthe convex hull 2404 b, and thus the arrangement 2402 a of ultrasoundelements may be considered separated in multiple dimensions in spacefrom the arrangement 2402 b of ultrasound elements.

Arrangements of ultrasound elements according to one or more aspects ofthe present application may take any suitable form. According to oneaspect, arrangements of ultrasound elements are configured on a support,and/or shaped substantially as paddles. A non-limiting example isillustrated in FIG. 25. As shown, the system 2500 includes a firstpaddle 2502 a and a second paddle 2502 b, each of which includes arespective arrangement of ultrasound elements 2504 a and 2504 b on arespective support 2510 a and 2510 b (also referred to herein assubstrates or mounts). Each paddle is connected to control andprocessing circuitry 2506 by a respective connection 2508 a and 2508 b(wired, wireless, and/or assuming any suitable form). The ultrasoundelements of paddle 2502 a may communicate with those of paddle 2502 b inthe manner previously described with respect to substantially opposedarrangements of ultrasound elements.

The supports 2510 a and 2510 b may be any suitable supports. They may berigid in some embodiments, and flexible in others. They may have anysizes suitable for accommodating the arrays 2504 a and 2504 b. Thesupports may be formed of any suitable material, such as plastic,rubberized materials, metal, and/or any other suitable material ormaterials. In some embodiments it may be desirable to use the paddles2502 a and 2502 b in combination with MRI technology (e.g., within anMRI machine), and thus it may be preferred in some embodiments for thesupports to be formed of non-magnetic material.

Constructing arrangements of ultrasound elements in the form of paddles,as shown in FIG. 25, may provide various benefits. For example, thepaddles may be movable and thus may facilitate positioning with respectto a patient or other subject of interest. For example, the paddles maybe handheld in some embodiments (e.g., using handles 2512 a and 2512 b)and therefore easily manipulated by a user. Furthermore, the paddles maybe portable, allowing for transport between locations (e.g., from roomto room in a hospital, or between other locations) and thereforeproviding convenient access to imaging technology.

The control and processing circuitry 2506 may be any suitable circuitryfor controlling operation and collection of data from the paddles 2502 aand 2502 b. For example, the control and processing circuitry 2506 mayembody any of the circuitry previously described herein, and may takeany suitable form.

FIG. 26 illustrates an alternative configuration of paddles to that ofFIG. 25. As shown, in the system 2600 the paddles are connected to arigid support 2602. The rigid support may facilitate maintaining thepaddles in a fixed relationship with respect to each other duringoperation, which may be desirable in some embodiments. The rigid support2602 may allow for movement of the paddles relative to each other, forexample in the direction of the arrows, as may be desired to repositionthe paddles when transitioning between analyzing different subjects orduring investigation of a single subject. The rigid support may take anysuitable form, and may be formed of any suitable material.

Adjustment of the positions of the paddles 2502 a and 2502 b along therigid support may be performed in any suitable manner, such as via aslide mount, or any other suitable manner According to a non-limitingembodiment, the rigid support 2602 may provide a force inwardly directedtoward the subject 2604, for example, to allow for a compression fit ofthe subject between the paddles 2502 a and 2502 b.

FIG. 27 illustrates a further embodiment in which communication betweenpaddles 2502 a and 2502 b is provided. As previously described, it maydesirable in some settings to determine a relative orientation and/orposition of the arrays 2504 a and 2504 b with respect to each other. Forexample, knowledge of the relative (and/or absolute) orientation and/orposition of the arrays may facilitate processing of data signalscollected by the elements of the arrays. In some embodiments, therelative orientation and/or position may be detected dynamically. FIG.27 illustrates multiple non-limiting examples of how the relativeorientation and/or position of the arrays may be determined.

According to a non-limiting embodiment, each of the paddles 2502 a and2502 b may include a respective one or more sensor(s) (or detector(s))2702 a and 2702 b. The sensors may operate to detect the relativeorientation and/or position of the respective paddle, in some casesdynamically. Additionally or alternatively, the sensors 2702 a and 2702b may detect an absolute orientation and/or position, in some casesdynamically. Non-limiting examples of suitable sensors includegyroscopes, accelerometers, inclinometers, range finders, inertialnavigation systems, lasers, infrared sensors, ultrasonic sensors,electromagnetic sensors, any other suitable sensors, or any combinationof two or more such sensors. In some embodiments, one or more of thesensors may be integrated with the ultrasound elements (e.g., configuredas ultrasound sources or ultrasound sensors) on a substrate. Thesensor(s) may be integrated on the substrate, for example by flip-chipbonding, flex-circuit bonding, solder bump bonding, monolithicintegration, or in any other suitable manner In some embodiments, theultrasound elements may be on a flexible support together with one ormore of the sensors.

According to a non-limiting embodiment, the sensors 2702 a and 2702 bmay communicate with each other, for example, to transmit signals toeach other indicative of orientation and/or position, or to transmitsignals from which relative orientation and/or position of the paddlesmay be determined. Communication between the sensors 2702 a and 2702 bmay be performed wirelessly, using any suitable wireless communicationprotocol.

Alternatively or additionally, the sensors 2702 a and 2702 b maycommunicate with a remote device 2704, which may process signals fromthe sensor 2702 a and/or 2702 b to determine relative and/or absoluteorientation and/or position of one or both of the paddles. Communicationbetween the sensors 2702 a and/or 2702 b and the remote device 2704 maybe performed wirelessly, using any suitable wireless protocol, or may beperformed in any other suitable manner.

The remote device 2704 may be any suitable device, such as ageneral-purpose processor. The remote device 2704 may be remote in thesense that it is distinct from the paddles 2502 a and 2502 b, but neednot necessarily be at a separate geographic location. For example,according to an embodiment, a system such as system 2700 may be employedin a medical office. The remote device 2704 may be, for example,disposed at a fixed location within the office, and the paddles 2502 aand 2502 b may be moved within the office as needed to position themrelative to a patient being examined. The remote device 2704 maycommunicate with one or both of the paddles 2502 a and 2502 b via thesensors 2702 a and 2702 b, or in any other suitable manner (e.g., viatransmitters distinct from the sensors, via wired connections, or in anyother suitable manner). As shown, the remote device 2704 may not onlyreceive signals from the sensors 2702 a and/or 2702 b, but also mayactively transmit signals to the sensors.

While FIG. 27 illustrates an embodiment in which both control andprocessing circuitry 2506 and a remote device 2704 are provided, not allembodiments are limited in this respect. According to an alternativeembodiment, the control and processing circuitry 2506 may perform thefunctionality of the remote device. Thus, the remote device is optionaland may not be included in all embodiments.

According to an alternative embodiment, determination of relativeorientation and/or position of the paddles 2502 a and 2502 b may beperformed without the need for sensors 2702 a and/or 2702 b. Forexample, suitable processing of ultrasound signals detected by theultrasound elements of arrays 2504 a and/or 2504 b may provide the sameor similar information. For example, suitable processing of such signalsmay indicate distance between the arrays 2504 a and/or 2504 b and mayalso be used to detect relative angles of the arrays, thus providingrelative orientation.

Thus, it should be appreciated that there are various manners in whichabsolute and/or relative orientation and/or position of multiple arraysof ultrasound elements, whether arranged in the form of paddles or not,may be determined. The various aspects described herein in whichdetection of relative orientation and/or position of arrangements ofultrasound elements is performed are not limited in the manner in whichthe orientation and/or position are determined.

According to an alternative non-limiting embodiment, an arrangement ofultrasound elements may be disposed on a flexible support. FIG. 28illustrates a non-limiting example, showing a system 2800 comprising afirst flexible support 2802 a and a second flexible support 2802 b. Eachof the flexible supports may have disposed thereon an arrangement 2804of ultrasound elements (e.g., the arrangement 2804 may be an array suchas 102 a and 102 b, or any other suitable arrangement of the typesdescribed herein). The supports may be formed of any suitable materialproviding a desired level of flexibility, such as flexible plastic, arubberized material, or any other suitable material. Again, it may bedesirable for the supports 2802 a and 2802 b to be formed of a materialwhich is non-magnetic, for example, to facilitate use of the system 2800in combination with MRI techniques.

Use of flexible supports such as those illustrated in FIG. 28 mayprovide various benefits. For example, use of flexible supports mayallow for positioning of arrangements of ultrasound elements whichconform to a subject, such as a patient's body. Thus, various imaginggeometries may be accommodated where use of a rigid support may not beadequate. As will be appreciated, the relative position betweenultrasound elements of an arrangement disposed on a flexible support,such as on support 2802 a, may change as the support is flexed. Forexample, some ultrasound elements of an arrangement disposed on support2802 a may become closer to each other when the substrate is flexed in afirst direction, or alternatively may become farther from each other ifthe substrate is flexed in a different direction. Thus, in processingdata collected from arrangements of ultrasound elements implemented onflexible supports, use of a suitable process which may account for suchvariation in the positioning among ultrasound elements may be preferred.Non-limiting examples of suitable processes are described further below.

As one non-limiting example, a compressive sensing image reconstructionprocess may account for variation in the positioning among ultrasoundelements when generating one or more volumetric images, as described inmore detail below. In some embodiments, a calibration procedure may beused to calibrate a system having arrays arranged on flexible supports.For instance, time of flight data collected using such a configurationof ultrasound elements as that shown in FIG. 28 may be fit to thegeometry of the supports using a second order polynomial (or othersuitable fitting technique) in the absence of a subject between theelements. The resulting fit may be treated as a baseline (or background)for operation of the system. Then, when data is collected of a subjectof interest using substantially the same configuration, the backgrounddata may be subtracted out.

According to an alternative embodiment, sensors which detect flexing maybe implemented in a system like that shown in FIG. 28. For example,variable resistance resistors whose resistance changes in response toflexing may be implemented on the supports 2802 a and 2802 b. When thesupports are flexed, the resistance value of such resistors may providean indication of the flexed geometry of the substrates, and thereforethe positioning (relative or absolute) of ultrasound elements disposedon the substrates. Other techniques for monitoring changes in geometryof arrangements of ultrasound elements on flexible supports may also beused.

In embodiments in which flexible supports are used, an array ofultrasound elements may be concave depending on the curvature of thesupport(s). In some embodiments, use of concave arrays of ultrasoundelements as sources and/or sensors may be desirable for purposesindependent of having the array conform to a subject. Ultrasoundelements located near the edge of an array of such elements may producewasted energy in that the some of the energy produced by such elementsmay radiate in directions not focused toward the subject. Thus, byorientating (e.g., angling) ultrasound elements located at the edges ofan array such that they are directed inward (toward the subject), energyefficiency gains may be realized. Accordingly, some embodiments of thepresent application provide concave arrays of ultrasound elements,whether achieved through suitable flexing of a flexible substrate onwhich the arrays are formed or through manufacture of a (rigid) concavesubstrate. Various manners of achieving a concave array of ultrasoundelements are possible.

As previously described, in some embodiments, an ultrasound-imagingdevice having multiple ultrasound sources and multiple ultrasoundsensors may be used to obtain measurements of a subject being imaged. Inturn, an image reconstruction process may be used to generate one ormore volumetric images of the subject from the obtained measurements.

Illustrative, non-limiting examples of image reconstruction processesthat may be used in accordance with embodiments of the presentapplication are described in greater detail below. In one embodiment, acompressive sensing image reconstruction process may be used tocalculate a volumetric image of the subject from measurements obtainedby an ultrasound imaging device.

In some embodiments, an image reconstruction process may be used toobtain a volumetric image of a subject by using measurements obtainedwhen the ultrasound imaging device is operated in a transmissivemodality. In these embodiments, as previously described, the ultrasoundsensors are configured to receive ultrasound signals which may betransmitted through the subject being imaged by multiple ultrasoundsources. The ultrasound sources may be disposed in an opposingarrangement to the ultrasound sensors, though the sources and sensorsmay be disposed in any of the arrangements described herein as aspectsof the present application are not limited in this respect.

By measuring characteristics (e.g., amplitudes, frequencies, and/orphases) of the ultrasound signals (or changes thereof) that pass throughthe subject being imaged, information related to the subject may beobtained to form a volumetric image of the subject. Such information maybe contained in measurements derived from the measured characteristics.Such measurements include, but are not limited to, attenuationmeasurements and time-of-flight measurements. Indeed, as previouslydescribed, the amplitude of a received ultrasound signal may be used toobtain a value indicative of an amount of attenuation of that ultrasoundsignal as result of its passing through the subject being imaged. Phaseof a received ultrasound signal may be used to obtain a value indicativeof the time-of-flight of the signal from the source that transmitted theultrasound signal to the ultrasound sensor that received it.

It should be appreciated that an image reconstruction process used toobtain a volumetric image of a subject is not limited to usingmeasurements obtained when the ultrasound imaging device is operated ina transmissive modality. For example, in some embodiments, the imagereconstruction process may use measurements obtained at least in partbased on scattered radiation such as back-scattered radiation and/orforward-scattered radiation.

In some embodiments, an image reconstruction process may be applied toall the measurements obtained by the ultrasound imaging device within aperiod of time. The period of time may be set in any of numerous waysand, for example, may be set to be sufficiently long so that a signaltransmitted from each of the ultrasound sources may be received by atleast one (or all) of the ultrasound sensors in the ultrasound imagingdevice. Though, it should be recognized that in some embodiments theimage reconstruction process may be applied to some, but not all, themeasurements obtained by the ultrasound imaging device within a periodof time, as aspects of the present application are not limited in thisrespect. This may be done for numerous reasons, for instance, when avolumetric image of only a portion of the subject being imaged isdesired.

In some embodiments, an image reconstruction process may take intoaccount the geometry of the sources and sensors in the ultrasoundimaging device to calculate a volumetric image of the subject frommeasurements obtained by the imaging device. To this end, the imagereconstruction process may utilize information about the geometry of thesources and sensors and such information may be obtained for use in theimage reconstruction process in addition to (and, in some embodiments,independently of) the measurements obtained from the signals received bythe ultrasound sensors. Though, in some embodiments, an imagereconstruction process may be applied to measurements to obtain avolumetric image without using any additional information about thegeometry of the sources and sensors used to obtain such measurements, asaspects of the present application are not limited in this respect.

Although any of numerous types of image reconstruction processes may beused, in some embodiments, a compressive sensing (CS) imagereconstruction process may be used to calculate a volumetric image ofthe subject from measurements obtained by an imaging device. A CS imagereconstruction technique may comprise calculating a volumetric image ofthe subject at least in part by identifying a solution to a system oflinear equations relating a plurality of measurements (e.g.,time-of-flight measurements, attenuation measurements, etc.) to aproperty of the subject being imaged (e.g., index of refraction, etc.).The system of linear equations may represent a linear approximation tothe forward operator of a three-dimensional wave propagation equation orequations. Accordingly, applying a CS image reconstruction techniquecomprises identifying a solution to a system of linear equations,subject to suitable constraints, rather than numerically solving awave-propagation equation in three dimensions, which is morecomputationally demanding and time consuming. A CS image reconstructionprocess may calculate a volumetric image of the subject, at least inpart, by using a domain (e.g., a basis) in which the image may besparse. Such a domain is herein referred to as a “sparsity domain”(e.g., a sparsity basis; though the domain need not be a basis and, forexample, may be an overcomplete representation such as a frame of avector space). An image may be sparse in a sparsity basis if it may beadequately represented by a subset of coefficients in that basis.Reconstruction processes taking into account the geometry of an imagingsystem may utilize any suitable algorithms, examples of which mayinclude diffraction-based algorithms. Others are also possible.

Some embodiments, where an image reconstruction process may take intoaccount the geometry of sources and sensors of the ultrasound imagingdevice, are described below with reference to FIG. 29. FIG. 29illustrates a non-limiting process 2900 for obtaining one or morevolumetric images from multiple measurements of a subject being imaged,in accordance with some embodiments. Process 2900 may be performed byany suitable processor or processors. For example, process 2900 may beperformed by the reconstruction computer described with reference toFIG. 4.

Process 2900 begins at stage 2902, where the information about thegeometry of sources and sensors in the ultrasound imaging device isobtained. In some instances, such geometry information may compriseinformation about the location of one or more ultrasound sources and/orone or more sensors in the ultrasound imaging device. The locationinformation may comprise any information from which a location of one ormore sources and/or sensors in three-dimensional space may be obtainedand, as such, may comprise absolute location information for one or moresources and/or sensors, relative location information for one or moresources and/or sensors, or both absolute information and relativeinformation. Absolute location information may indicate the location ofone or more sources and/or sensors without reference to location ofother objects (e.g., sources, sensors, other components of theultrasound imaging device, etc.) and, for example, may includecoordinates (e.g., Cartesian, spherical, etc.) indicating the locationof one or more sources and/or sensors in three-dimensional space.Relative location information may indicate the location of one or moresources and/or sensors with reference to the location of other objectsand, for example, may indicate the location of one or more sourcesand/or sensors relative to one or more other sources and/or sensors.

In some instances, when the ultrasound imaging device has one or morearrays of sources and/or sensors, the geometry information may compriseinformation about the location and/or orientation of each such array inthree-dimensional space. As one non-limiting example, in embodimentswhere the ultrasound imaging device comprises sources and sensorsdisposed on moveable supports (e.g., a pair of hand-held paddles as inFIG. 25), the geometry information may comprise information about thelocation and/or orientation of one or more of the moveable supports. Thelocation information may comprise absolute location information for oneor more arrangements, relative location information for one or morearrangements, or any suitable combination thereof. Absolute locationinformation may indicate the location and/or orientation of anarrangement without reference to location of other objects (e.g., anyother arrays or components of the ultrasound imaging device) and, forexample, may include coordinates indicating the location and/ororientation of the arrangement in three-dimensional space. Relativelocation information may indicate the location and/or orientation of anarrangement relative to that of another array or component of theultrasound imaging device.

Geometry information may be obtained at 2902 in any of numerous ways. Asdescribed in more detail below, the geometry information may be obtainedby using one or more sensors (e.g., accelerometer, gyroscope,inclinometer, inertial navigation system, etc.) in the ultrasoundimaging device or outside the ultrasound imaging device. Moreover, asdescribed in more detail below, geometry information may be obtained,additionally or alternatively, by operating the ultrasound imagingdevice in a transmissive modality to obtain the geometry informationfrom characteristics of the signals received by the sensors of theimaging device. This may be done before the ultrasound imaging device isused to image a subject, but may be done, additionally or alternatively,while the ultrasound imaging device is being used to image the subject(e.g., dynamically during operation of the ultrasound imaging device).

Regardless of the manner in which geometry information is obtained in2902, process 2900 next proceeds to 2904, where a geometric model isconstructed based, at least in part, on the obtained geometryinformation. The constructed geometric model represents the obtainedgeometry information and, in some instances, may represent the geometryinformation so that it may be used by one or more image reconstructionprocesses.

In some embodiments, the geometric model may comprise path lengthinformation for one or more pairs of ultrasound sources and sensors. Foran ultrasound source-sensor pair, a line segment between (positions of)the ultrasound source and the ultrasound sensor may intersect one ormore voxels in the volume being imaged. For each of one or more suchvoxels, the path length information may comprise a value indicative of alength of the portion of the line segment that intersects the voxel. Forexample, as shown in FIG. 30, a voxel r lies along a line segment fromsource r₀ to sensor r₁. The length of the portion of the line segmentintersecting the voxel r is shown to be l. As such, in this illustrativeexample, the path length information may comprise the value l.Additionally or alternatively, the path length information may identifyone or more voxels of the volume being imaged, which intersect a linesegment from the ultrasound source and to the ultrasound sensor.

In some embodiments, the path length information may comprise valuesindicative of the lengths of portions of a line segment between anultrasound source and the ultrasound sensor for every source-sensor pair(i.e., every pair of an ultrasound source and an ultrasound sensor inwhich the ultrasound sensor may detect a signal transmitted by theultrasound source). The values may include a value for each of one ormore voxels intersecting the corresponding line segment.

The path length information may be calculated based at least in part onthe geometry information obtained in 2902. In some embodiments, a valueindicative of a length of the portion of the line segment thatintersects a voxel may be calculated based, at least in part, on thegeometry information obtained in 2902. The distance may be computedbased on location information, absolute and/or relative, of theultrasound source, the ultrasound sensor, and the voxel. As anon-limiting example, this distance may be computed by using coordinates(in any suitable coordinate system) specifying the locations of theultrasound source, ultrasound sensor and the voxel.

Values included in path length information may be organized in anysuitable way for accessing and using those values for subsequentprocessing. To this end, in some embodiments, the values may be encodedin a data structure. The data structure encoding such values may bestored on any tangible computer-readable storage medium (e.g., acomputer hard drive, a CD, a flash memory, EEPROM, magnetic tape, disk,static RAM, dynamic RAM, or any other suitable medium). The listed typesof computer-readable storage media are non-limiting examples ofnon-transitory storage media, and thus it should be appreciated thatnon-transitory storage media may be used in some embodiments. Thecomputer-readable storage medium may be accessed by any physicalcomputing device that may use the values encoded in the data structure.

By way of an illustrative non-limiting example, path-length informationmay be encoded in a matrix data structure, commonly referred to as amatrix. The matrix may have an entry for each value, included in pathlength information, which is indicative of a length of a line segmentthrough a voxel in a volume being imaged. For example, the matrix mayhave a row (or column) storing values for each ultrasound source-sensorpair. In embodiments, where the ultrasound device has a source arrayhaving N×N (N²) elements and a sensor array having N×N (N²) elements,the matrix may have up to N⁴ rows (or columns) as there are up to N⁴source-sensor pairs in such an arrangement. It should be appreciatedthat the source array is not limited to having a square-like N×Narrangement of elements, and may have N_(tx)×N_(ty) array of sources andan N_(rx)×N_(ry) array of sensors. In this case, the matrix may have upto N_(tx)×N_(ty)×N_(rx)×N_(ry) rows (or columns) as there up toN_(tx)×N_(ty)×N_(rx)×N_(ry) source-sensor pairs. For ease ofpresentation we denote this matrix by the symbol A.

Each row (or column) of the matrix A may comprise values indicative ofthe lengths of the portions of a line segment, between the source andsensor in the source-sensor pair associated with the row, through thevoxels corresponding to each entry in the row. As a specific example, ina case when a volume being imaged comprises a volume composed ofM_(x)×M_(y)×M_(z) voxels, each row (or column) of matrix A may haveM_(x)×M_(y)×M_(z) entries (or M³ entries when M_(x)=M_(y)=M_(z)). Assuch, in this illustrative non-limiting example, the geometric modelconstructed in act 2904 from obtained geometry information may comprisepath length information, which may be encoded in an N⁴×M³ matrix A whoseentry at (ijkl)'th row (i.e., the row associated with source (i,j) andsensor (k,l)) and (xyz)'th column (i.e., the column associated withvoxel at coordinate (x,y,z) in the volume being imaged) corresponds to avalue indicating the length of a path up through voxel (x,y,z) of a raygoing from source (i, j) to receiver (k, l).

Entries of the matrix A may be computed in any of numerous ways. As oneillustrative non-limiting example, a length of a portion of a linesegment (from a source to a sensor in a source-sensor pair) through avoxel may be iteratively computed (in serial or in parallel) for each ofmultiple voxels in a volume being imaged and for each of multipleultrasound source-sensor pairs. In some cases, a length of a portion ofa line segment may be computed for each voxel in a volume being imagedand for each ultrasound source-sensor pair in the ultrasound imagingdevice. In some embodiments, such a computation may be performed by (1)iterating over all voxels in the volume being imaged and, for each voxelin the volume, (2) iterating over all ultrasound source-sensor pairsand, for each pair, (3) checking whether a line segment between thesource and the sensor in the pair intersects the voxel, and, if it does,then (4) computing a length of the portion of the line segment thatintersects the voxel.

The computational complexity of an approach in which the length of aline segment through a voxel is computed may scale linearly with theproduct of the number of source-sensor pairs and voxels in the volumebeing imaged. For example, in a case when a volume being imaged iscomposed of O(M³) voxels and there are O(N⁴) source-sensor pairs, thecomputational complexity of such an approach is O(N⁴M³) operations.Here, the “O(.)” notation is the standard “big O” notation, as is knownin the art. It should be recognized that numerous other approaches tocalculating entries of the matrix A are possible and, as described inmore detail in Appendix A below, some of these other approaches may havebetter computational complexity. For instance, in one such illustrativeapproach described in Appendix A, entries of the matrix A may becomputed by using a process whose computational complexity is O(N⁴M)rather than O(N⁴M³) as the case may be for the above-describedcalculation technique.

Moreover, in some embodiments, construction of the geometric model at2904 may take into account various physical phenomena. For example,scattering (e.g., back-scattered radiation, forward-scatteredradiation), dispersion, diffraction, and/or refraction may be taken intoaccount as desired. For example, dispersion may be modeled as a Taylorexpansion series, and may be accounted for in speed of sound andattenuation measurements. Accounting for such phenomena may provide moreaccurate geometric models and therefore more accurate images. However,not all embodiments require consideration of such phenomena.

In some embodiments in which line segment lengths are computed, suchcomputation may take into account refraction. Doing so may improve theaccuracy of a reconstructed image, for example by reducing smearing inthe image. In many embodiments, assuming a straight line from a sourceto a sensor represents an approximation. In practice, the path fromsource to sensor may deviate from a straight line due to refraction. Onemanner of accounting for the impact of refraction is to utilize aniterative reconstruction process.

A volumetric image may be reconstructed initially assuming straightpaths from sources to sensors of an imaging system. Refracted paths maythen be computed in any suitable manner According to some embodiments,refracted paths may be computed using Fermat's principle, for example byformulating a suitable differential equation based on the principle andobtaining a solution to the differential equation. The differentialequation may be formulated to represent optic ray propagation in two orthree dimensions. The different equation may be formulated at least inpart based on the Euler-Lagrange equations. The computed refracted pathsmay then be used to calculate another volumetric image of the subject.

Accordingly, in some embodiments, an iterative reconstruction processmay comprise accessing measurements of a subject; calculating a firstvolumetric image of the subject from the accessed measurements and usingfirst path length information obtained by assuming straight paths fromsources to sensors of the ultrasound imaging device used to obtain themeasurements (e.g., in a transmissive modality); computing refractivepaths and using the refractive paths to calculate second path lengthinformation; and calculating a second volumetric image of the subjectfrom the measurements and the second path length information.

In some embodiments, where a compressive sensing image reconstructiontechnique is used to calculate volumetric images of the subject, and thetechnique includes identifying a solution to a system of linearequations relating measurements of the subject to a property of thesubject being imaged, the system of linear equations may be modified toaccount for the computed refracted paths. As one non-limiting example,the above-described matrix A (representing the system of linearequations) may be modified to account for the refracted paths. Theresulting updated system of linear equations may be used to calculateanother volumetric image of the subject. As desired, the method may beiterated (e.g., by again calculating the refracted paths and againupdating the matrix A) as many times as needed to provide a desiredlevel of accuracy of the reconstructed image.

As mentioned, path lengths, as well as path shapes, may be calculated inany suitable manner In some embodiments, the path lengths and/or pathshapes may be calculated over a discretized grid by using Dijkstra'salgorithm, Floyd-Warshall algorithm, and/or Johnson's algorithm may beused. In other embodiments, ray-tracing (e.g., ray-bending) techniquesmay be used. Other techniques are also possible.

Regardless of how the geometric model is constructed from geometryinformation at 2904, process 2900 proceeds to 2906, where measurementsof a subject being imaged are obtained. Measurements of the subject maybe obtained in any suitable way. In some embodiments, the measurementsmay be accessed after having been obtained by using an ultrasoundimaging device (e.g., operating in a transmissive modality) and madeavailable for subsequent access. Additionally or alternatively, themeasurements may be obtained by using the ultrasound imaging device aspart of act 2906. In some embodiments, the measurements may be obtainedbased at least in part on energy forward scattered from the subject anddetected by the ultrasound imaging device.

Any of the numerous types of measurements previously described herein orany other measurements may be obtained including, but not limited to,amplitude of the received ultrasound signals, phase of the receivedultrasound signals, frequency of the ultrasound signals as well as anymeasurements (e.g., attenuation, time-of-flight, speed of sound,temperature, etc.) derived from these quantities. The measurements maybe received for some or all of the ultrasound sensors in an ultrasoundimaging device.

Since one or multiple of the above-described types of measurements maybe obtained as a result of the operation of an ultrasound imagingdevice, one or multiple volumetric images may be obtained by applying animage reconstruction process to these measurements. In some embodiments,a volumetric image of the subject being imaged may be calculated fromeach of one or more of the above-described types of measurements. Forexample, a volumetric image of the subject being imaged may becalculated based at least in part on time-of-flight measurements. Insome instances, such a volumetric image may be a volumetric image of theindex of refraction of the subject being imaged, herein referred to as avolumetric index of refraction image. Additionally or alternatively, avolumetric image may be calculated based, at least in part, on theattenuation measurements, herein referred to as a volumetric attenuationimage. Additionally or alternatively, a volumetric image may becalculated based, at least in part, on the speed-of-sound measurements,herein referred to as a volumetric speed-of-sound image. Additionally oralternatively, a volumetric image of the subject being imaged may beformed based, at least in part, on temperature measurements, hereinreferred to as a volumetric temperature image. Any suitable number ofvolumetric images may be calculated from the obtained measurements, asaspects of the present application are not limited in this respect.

After measurements are obtained, process 2900 proceeds to 2908, where animage reconstruction process may be used to generate one or morevolumetric images from the obtained measurements. Any suitable imagereconstruction process may be used. In some embodiments, an imagereconstruction process that takes into account the geometry information(obtained at 2902) and/or the geometric model (constructed at 2904) maybe used. The image reconstruction process may use the geometryinformation and/or the geometric model to calculate a property of thesubject being imaged from the measurements obtained at 2906 and, in someembodiments, may calculate a value associated with the property for eachof one or more voxels in a volume being imaged in order to calculate avolumetric image. For example, in some embodiments, a geometric modelcomprising path length information may be used to compute an index ofrefraction for each of one or more voxels in a volume being imaged fromtime-of-flight measurements only, from attenuation measurements only, orfrom both time-of-flight measurements and attenuation measurements. Inembodiments where both time-of-flight and attenuation measurements areused to compute an index of refraction, the calculation may be done atleast in part by using Kramers-Kronig relations and/or power lawcalculations to relate attenuation measurements with time-of-flightmeasurements. As another example, in some embodiments, an imagereconstruction process may use a geometric model comprising path lengthinformation to compute a scattering and/or absorption value for each ofone or more voxels in a volume being imaged from the attenuationmeasurements only, time-of flight measurements only, or from bothtime-of-flight measurements and attenuation measurements.

A geometric model comprising path length information may be used torelate measurements to a property of the subject being imaged in any ofnumerous ways. In some embodiments, the path length information may beused to construct a functional relationship (i.e., a mapping) betweenthe measurements and the property of interest. This may be accomplishedin any of numerous ways. As an illustrative non-limiting example, thepath length information may be used to construct a mapping between thetime-of-flight measurements and indices of refraction of voxels in anvolume being imaged by using the above-described matrix A. Inparticular, suppose that the matrix A has N⁴ rows, with each rowcorresponding to an ultrasound source-sensor pair (for opposedrectangular arrays of dimension N×N), and M³ columns, with each columncorresponding to a voxel being imaged (for a cubic volume of dimensionM×MxM). Additionally, let x be an M³×1 vector of index of refractionvalues for each of the voxels in the volume being imaged, and let y bean N⁴×1 vector of time-of-flight measurements (with each measurementobtained from a source-sensor pair). Then the measurements may berelated to the index of refraction values according to the relationshipgiven by:

Ax=y,  (1)

Thus, the linear relationship of (1) may be used to calculate avolumetric image by obtaining the measurements y and using (1) toestimate x, which contains the values of one or more voxels of thevolumetric image. It should be appreciated that a relationship analogousto that of (1) may be constructed for any of the above-described typesof measurements and properties. It should also be appreciated that thedimensions of the above matrices and vectors are illustrative andnon-limiting, as the precise dimensions of the vectors and matrices maydepend on the number of source-sensor pairs used to obtain measurementsas well as the number of voxels for which a value of the property ofinterest is to be calculated. It should also be appreciated that therelationship between properties of the subject being imaged is notlimited to being represented in a form such as (1) and, in someembodiments, may be represented in any other suitable way.

Any of numerous image reconstruction processes may be used to calculatea volumetric image by using the measurements obtained at 2906 and ageometric model comprising path length information. For example, anyimage reconstruction process that may be used to calculate a volumetricimage based, at least in part, on the relationship (1) may be used. Insome embodiments, a compressive sensing (CS) image reconstructionprocess may be used to generate a volumetric image by using a geometricmodel comprising path length information and the measurements obtainedat 2906 and, for example, based, at least in part, on the relationship(1).

Compressed sensing or compressive sampling refers to a set of signalprocessing techniques (e.g., image processing techniques) premised onthe assumption that the signals to which they are applied are sparse insome sparsifying domain That is, the energy of these signals may beconcentrated in a small subset of the sparsifying domain For example,images may be sparse (and as a result may be amenable to beingcompressed) in certain domains A typical photograph, for instance, maybe sparse in the Discrete Cosine Transform (DCT) domain because most ofthe energy in the DCT coefficients is concentrated in a small subset ofthe DCT coefficients representing the photograph in the transformdomain, while the other coefficients are either zero or very small withrespect to the largest coefficients. Thus, the DCT is a “sparsifying”’transform for natural images—which is one reason that it is thetechnique underlying JPEG compression. Another sparsifying transform isthe CDF Wavelet Transform, which is the technique underlying JPEG 2000compression.

As another example, medical images may be sparse in the DCT domain FIG.31 shows how images of the brain may be compressed by discarding datacorresponding to, e.g., the smallest N % DCT coefficients, where N isany number between 0 and 100. As an illustrative example, FIG. 31 showsimages of the brain at various levels of “compression” in the DCT domainTo obtain the images shown in a particular column of images shown inFIG. 31, the original brain images are transformed to the DCT domain,all N % (where N is indicated at the top of the column) of the DCTcoefficients representing the transformed images are discarded, and theimages shown in FIG. 31 are reconstructed from the remaining DCTcoefficients. Note how similar the images are across columns even aslarge percentages of coefficients are discarded. Indeed, many of theimportant features in the images are still discernible even when 99% ofthe coefficients are discarded, demonstrating that medical images may besparse in the DCT domain.

Accordingly, a compressive sensing image reconstruction processutilizing a sparsity domain to generate the volumetric image from theobtained measurements may be used at 2908. The sparsity domain may beany suitable domain in which the volumetric image may be sparse. In someembodiments the sparsity domain may be a representation such as a basis,a frame of a vector space, an overcomplete representation, etc., inwhich the volumetric image may be sparse. For example, the sparsitydomain may be a three-dimensional basis including, but not limited to, athree-dimensional generalization of any type of discrete cosine basis,discrete sine basis, wavelet basis, or any other type of sparsifyingdomain known in the art. As a particular non-limiting example, thethree-dimensional discrete cosine transform, which is thethree-dimensional generalization of the DCT-II, or D₃ for short, isgiven according to:

${\left( {D_{3}x} \right)_{k} = {{\sum\limits_{n = 0}^{N - 1}\; {a_{n}\cos \frac{\pi \; k}{N}n}} + {\frac{1}{2}x_{n}}}},{where}$$a_{n} = \left( \begin{matrix}\frac{1}{\sqrt{N}} & {n = 0} \\\frac{1}{\sqrt{2\; N}} & {n > 0.}\end{matrix} \right.$

A compressive sensing image reconstruction process may generate avolumetric image based, at least in part, on the measurements (e.g.,obtained at 2906), geometric model (e.g., calculated at 2904), and thesparsity basis. This may be done in any suitable way. In someembodiments, a compressive sensing image reconstruction process maycalculate a volumetric image by using a mapping between the measurements(e.g., time-of-flight measurements) and a property of the subject beingimaged (e.g., indices of refraction). As an illustrative example, a CSimage reconstruction process may use the relationship (1) together witha sparsity basis to calculate a volumetric image. In some embodiments, aCS image reconstruction process may calculate a volumetric image atleast in part by solving an optimization problem comprising a sparsityconstraint. In one illustrative, non-limiting embodiment this may bedone, at least in part, by solving:

min∥x∥ _(l) ₁ , subject to the constraint of (AD ₃ ⁻¹)x=y,  (2)

and return x*=D₃ ⁻¹x as the vector of values corresponding to thevolumetric image, where the matrix A and the vectors x and y, werepreviously described with reference to (1). This formulation ofcompressive sensing is sometimes called the basis pursuit method andcomprises optimizing an l₁ norm subject to an equality constraint. Itshould be appreciated that a CS image reconstruction process may be usedto calculate a volumetric image at least in part by solving optimizationproblems different from that of (2), corresponding to differentformulations of compressive sensing. For example, a CS imagereconstruction process may calculate a volumetric image at least in partby optimizing an l₁ norm subject to an inequality constraint (e.g.,minimize ∥x∥_(l1) subject to ∥AD₃ ⁻¹x−y∥₂<λ, for some small λ>0, where ∥∥₂ is the Euclidean norm, and where ∥ ∥_(l1) is the l₁ norm). As anotherexample, a CS image reconstruction process may calculate a volumetricimage at least in part by using the Dantzig selector approach (e.g.,minimize ∥x∥_(l1) subject to ∥A*(AD₃ ⁻¹x−y)∥∞<λ, where A* is theHermitian conjugate of A and ∥ ∥∞ is the 1∞ norm). As yet anotherexample, a CS image reconstruction process may calculate a volumetricimage at least in part by using an objective function comprising atotal-variation norm (e.g., minimize ∥x∥_(l1)+α∥x∥_(TV) subject to ∥AD₃⁻¹x−y∥₂<λ, for some small λ>0, for some α>0, where ∥ ∥_(TV) is the totalvariation norm suitably generalized to three dimensions). As yet anotherexample, a CS image reconstruction process may calculate a volumetricimage at least in part by using a LASSO algorithm (e.g., minimize ∥AD₃⁻¹x−y∥₂ subject to ∥x∥_(l1)<λ, for some small λ>0). As yet anotherexample, a CS image reconstruction process may calculate a volumetricimage at least in part by using an objective function comprising are-weighted l₁ norm subject to any of the above-described constraints orany other suitable constraints. Other examples of compressive sensingtechniques that may be used as part of a CS image reconstruction processinclude, but are not limited to, soft thresholding, hard thresholding,matching pursuit, and iterative greedy pursuit. Thus, it should beappreciated that the formulation of (2) is an illustrative andnon-limiting example.

It should be appreciated that solving (2) may be considered a proxy forreconstructing the unknown volumetric image x from a set of measurementsy, such that x is the sparsest signal consistent with the measurements.Indeed, under certain conditions, minimizing the l₁ norm subject to aconstraint by solving:

min∥Ψx∥ _(l) ₁ , s·t·Ax=y,  (2a)

where ∥x∥_(l) ₁ =Σ_(i=1) ^(n)|x| and Ψ is a sparsity basis (e.g., DCT),is equivalent to solving:

min∥Ψx∥ _(l) ₁ , s·t·Ax=y,

where the l₀ norm, is equal to the number of non-zero elements in x. Theformulation in (2a) may also be generalized according to alternative CSformulations (e.g., l₁ norm subject to inequality constraints, theDantzig selector, LASSO, etc.) as described with respect to equation(2). As such, it should be appreciated that the calculated volumetricimages may be sparse in the sparsity domain defined by Ψ. Note that thelatter problem, is a combinatorial optimization problem that iscomputationally infeasible, whereas the former (i.e., the optimizationproblem defined by (2a)) may be solved using any of numerous linearprogramming techniques as described in more detail below.

A CS image reconstruction process may utilize a suitable numericaltechnique or techniques to calculate a volumetric image. In someembodiments, any suitable convex optimization techniques may be used.For example, linear programming techniques may be used. As anotherexample, “first-order” methods such as Nesterov methods may be used. Asyet another example, interior point methods may be used. Such convexoptimization methods may be implemented at least in part by using“matrix-free” solvers such as a conjugate-gradient process, which may beadvantageous in a setting where it may be more efficient to operate onrows or columns of the matrix (AD₃ ⁻¹) than on the entire matrix, whichmay be the case when A is sparse and/or the sparsifying transform (e.g.,the DCT transform) may be efficiently computed using the fast Fouriertransform. It should be appreciated that techniques from sparse linearalgebra may be applied as well since the matrix A may be sparse. Indeed,the number of voxels intersecting a straight line through a cubic volumeV is O({square root over (V)}), so that each row (representing a singlemeasurement), may be largely filled with zeros.

Accordingly, a CS image reconstruction process may utilize one or moresoftware packages implementing the above-described numerical techniques.For example, a CS image reconstruction process may use one or morecompressive sensing software packages, numerical linear algebra softwarepackages, or other suitable software. In addition, a CS imagereconstruction process may be parallelized. An interior point method maycomprise performing multiple iterations of solving a particular linearequation, which may be done at least in part by using the conjugategradient (CG) algorithm or any other least squares solver. Such a CGalgorithm may be parallelized and may be performed by multipleprocessors and/or by a graphical processing unit or units. In someembodiments, a truncated CG technique may be used.

It should be recognized that a volumetric image may be calculated usingimage reconstruction processes other than compressive sensing imagereconstruction processes, as aspects of the present application are notlimited in this respect. For example, in some embodiments, aleast-squares type technique may be used. A least-squares type techniquemay be used with or without regularization. A least-squares typetechnique may be used to calculate a volumetric image at least in partby finding the solution x that minimizes the l₂ error (i.e., the squarederror) of the measurements according to:

min∥Ax−y∥ _(l) ₂ .  (3).

The relation (3) may be solved using any of numerous processesincluding, but not limited to, processes for iteratively solving linearequations such as the conjugate gradient process, LSQR process, etc.Though, it should be appreciated that the applicability of such atechnique may depend on whether the system of linear equationsrepresented by (1) is solvable. The relation (1) is one that maycomprise O(N⁴) equations in O(M³) variables and, depending on the valuesof M and N in a particular embodiment, may be over-constrained.

The inventors have appreciated that, in some instances, the solution to(3) may not be unique. That is, calculating a volumetric image by using(3) to compute x may be an ill-posed problem. Accordingly, in someembodiments, the least-squares criterion of (3) may be used togetherwith a regularization technique to identify a solution from among theset of non-unique solutions such that the identified solution satisfiesa suitable regularity criterion. Any of numerous regularizationtechniques (e.g., Tikhonov regularization, truncated SVD, totalvariation, edge preserving total variation, etc.) may be used, asaspects of the present application are not limited in this respect.

Regardless of the type of image reconstruction process used at 2908,process 2900 next proceeds to 2910 where the volumetric image(s)calculated at 2908 may be output. This may be done in any suitable way.In some embodiments, the calculated images may be presented for viewingby a user or users using one or more display screens or any other devicefor visualizing the images (e.g., a doctor viewing medical images).Additionally or alternatively, the calculated images may be stored(e.g., in a memory or any other suitable computer-readable storagemedium) so that they may be accessed later and presented for viewing bya user or users.

Once an image is generated, the image may optionally be manipulated. Forinstance, a viewer (e.g., a doctor) may desire to enlarge an image,shrink an image, move an image from side to side, and/or rotate an image(in 3D or otherwise), as non-limiting examples. Such manipulation may beperformed in any suitable manner, as the aspects described herein inwhich manipulation of an image is provided are not limited to the mannerin which the manipulation is performed.

For instance, an image may be manipulated via a user interface or otherdevice. A keyboard may be implemented, a mouse, a remote control, or a3D detection mechanism detecting movements of the viewer (e.g., handmovements) suggestive of the viewer's desired manipulation of the image.A non-limiting example of such 3D detection mechanisms is the Leap,available from Leap Motion of San Francisco, Calif. Such technology mayallow the viewer to control the image by pointing, waving, or usingother natural hand gestures within a detection space located above theLeap device.

Manipulation of images, performed in any suitable manner, may facilitatevarious functions to be performed by a user. For example, a doctorviewing such images may more easily be able to diagnose a patient basedon what is shown by suitable manipulation of the image. The doctor maybe able to plan a surgical path based on the image, or identify aposition of a patient at which to apply HIFU (described further below).Thus, various benefits may be achieved by allowing for viewing andmanipulation of images.

Next, process 2900 proceeds to decision block 2912, where it may bedetermined whether there are more measurements to be processed. In someembodiments, the ultrasound imaging device may obtain or may havealready obtained more measurements to use for forming one or moreadditional volumetric images. This may occur in numerous scenarios suchas when the imaging device is operated to obtain multiple volumetricimages of a subject being imaged. If it is determined, in decision block2912, that there are no additional measurements to be processed, process2900 completes.

On the other hand, if it is determined, in decision block 2912, thatthere are additional measurements to be processed, process 2900proceeds, via the YES branch, to decision block 2914, where it isdetermined whether the geometry of sources and/or sensors in theultrasound imaging device changed. In particular, it may be determinedwhether the relative position and/or orientation of the ultrasoundsources and sensors changed. This may be done in any suitable way and,for example, may be done based at least in part on information gatheredby one or more sensors configured to detect changes in the relativeposition and/or orientation of ultrasound sources and sensors (e.g., seeFIG. 27). Such sensors may be external to or onboard the ultrasoundimaging device, or at any other suitable locations.

If no change in the geometry of the sources and/or sensors is detected,process 2900 loops back, via the NO branch, to 2906 and 2906-2912 may berepeated. On the other hand, if a change in the geometry of the sourcesand/or sensors is detected, process 2900 loops back, via the YES branch,to 2902, where updated geometry information for sources and/or sensorsmay be obtained.

It should be appreciated that process 2900 is illustrative and manyvariations of this process are possible. For example, in the illustratedembodiment, process 2900 comprises obtaining geometry information andcalculating a geometric model based at least in part on the obtainedgeometry information. However, in other embodiments, a geometric modelmay have been pre-computed and saved in a memory or any other suitablecomputer-readable storage medium prior to the start of process 2900. Inthese embodiments, the pre-computed geometric model may be loaded ratherthan calculated as part of process 2900. Other variations are alsopossible.

In some embodiments in which compressive sensing techniques are used,the A matrix may be stored in memory. In some embodiments, the A matrixmay be stored in cache. In some embodiments, the A matrix may becomputed dynamically, for example by computing a kernel as a startingpoint. Thus, those embodiments utilizing compressive sensing techniquesare not limited in the manner in which the A matrix is obtained.

The physical process that takes place when a signal is transmitted froma radiation source to a radiation sensor may be modeled in any ofnumerous ways. For example, infinite wavelength approximations, such asthe straight ray approximation described earlier may be used.Higher-order approximations incorporating scattering and diffractionphenomena may also be used. For example, fat beams, Fresnel zone beams,Gaussian beams, banana-donut beams, and combinations of those types ofbeams may be implemented in the image reconstruction process to modelthe measurement process. As has been previously described, beamformingmay be implemented according to embodiments of the present application.Information about the beam may be used in the reconstruction process.For example, the beam type may impact the geometry of the system, andtherefore the above-described A matrix. Accordingly, in someembodiments, the A matrix may be computed to reflect the type of beamchosen for image reconstruction.

Compressive sensing is one technique which may be used to form imagesaccording to embodiments of the present application, as described above.However, other techniques may be used as well. As one example, one ormore algebraic reconstruction techniques (e.g., simultaneous algebraicreconstruction techniques (SART), filtered backprojection, etc.) may beused to form images. As another example, in some embodiments imagingconfigurations may be modeled as a forward scattering problem andvolumetric images may be calculated by using one or more inversescattering techniques (e.g., inverse scattering techniques using a Bornapproximation(s), Rytov approximation(s), hybrid Rytov approximation(s),series solutions, iterated solutions, and/or any suitable combinationthereof). The forward scattering problem may be evaluated numerically oranalytically, and does not require use of an A matrix. In someembodiments, modeling the system as a forward scattering problem mayallow for measuring the spatial frequencies of the index of refractionof a subject. For example, a value representing the gradient of theindex of refraction may be obtained for one or more voxels within animaged volume, thus providing an indication of the object susceptibilityor scattering potential of the object. As another example, in someembodiments, volumetric images may be calculated by using one or morewave-propagation techniques for propagating waves in three dimensions.For example, backpropagation techniques may be used. As another example,linearized backpropagation techniques (e.g., in the Fourier domain),iterative propagation techniques, pre-condition wave propagationtechniques, techniques utilizing Frechet derivative(s) of a forwardoperator, and/or time-reversed wave propagation techniques may be used.

Various aspects of the present application have been described in thecontext of imaging, and more specifically in the context of medicalimaging. For example, aspects of the present application may be used inthe diagnosis, monitoring, and/or treatment of patients. Detection ofvarious patient conditions, such as the presence of tumors, may befacilitated using one or more aspects of the present application.

However, it should be appreciated that medical imaging represents anon-limiting example of an application of the aspects described herein.

Moreover, techniques for ultrasound imaging described herein may beimplemented in combination with other medical imaging modalities. Aspreviously alluded to, another common imaging modality is MRI. MRI istypically characterized by drawbacks such as expense and geometryconstraints. MRI machines are conventionally large, and not easilyadapted to a subject under investigation. In some scenarios, it may bedesirable to provide an additional imaging modality in combination withMRI. One or more aspects of the present application may facilitate suchcombination of imaging modalities. For example, use of arrangements ofultrasound elements in the form of paddles (e.g., see FIGS. 25 and 26)may be used in combination with MRI. The paddles may be disposed in asuitable location with respect to a patient inside an MRI machine. Thedata collected by the arrangement of ultrasound elements and any imagesdeveloped therefrom may supplement MRI images.

It should be appreciated, however, that medical imaging represents anon-limiting field in which aspects of the present application may beapplied. For example, aspects of the present application may also beapplied to materials investigation, geologic investigation, and otherfields in which it is desired to determine properties of a subject ofinterest non-invasively.

Moreover, it should be appreciated that while various non-limitingembodiments have been described in the context of ultrasound, variousaspects of the present application are not limited in this respect. Forexample, some of the aspects of the present application may apply toother types of signals, such as X-ray techniques and opticaltransmission techniques, among others. Thus, it should be appreciatedthat arrangements of elements as described herein are not necessarilylimited to the elements being ultrasound elements, and the transmissionand reception of signals by arrangements of elements is not limited tosuch signals being ultrasound signals.

FIG. 32 illustrates a non-limiting example of a system 3200 as may beused according to one or more aspects of the present application forimaging of a patient. As shown, the system 3200 includes arrangements ofultrasound elements 3202 a and 3202 b, which may be configured aspaddles (e.g., of the type previously illustrated with respect to FIGS.25 and 26, or any other suitable type), though not all embodiments arelimited in this respect. The arrangements of ultrasound elements 3202 aand 3202 b may be disposed in a desired position with respect to apatient 3204 on a table 3206. The arrangements of ultrasound elements3202 a and 3202 b may be coupled via respective connections 3209 a and3209 b to a processing system 3208, which may be any suitable processingsystem, such as any of those previously described herein, forcontrolling operation of the arrangements of ultrasound elements.According to an embodiment, the processing system 3208 may further beconfigured to reconstruct one or more images. As shown, the processingsystem 3208 may be configured to receive a digital video disc (DVD) orcompact disc (CD) 3210, which may, in some non-limiting embodiments,store instructions which may be executed by the processing system 3208to control operation of the arrangements of ultrasound elements 3202 aand 3202 b. The processing system 3208 may itself include memory, forexample, random access memory (RAM), read-only memory (ROM), or anyother suitable memory. The memory may store instructions which may beexecuted by the processor 3208 to control operation of the arrangementsof ultrasound elements and/or to reconstruct one or more images of thesubject 3204.

In some embodiments, it may be desirable to provide for an acousticimpedance matching condition of the ultrasound device. For example, anacoustic impedance matching component may be positioned between anarrangement of ultrasound elements and a subject (e.g., a patient).FIGS. 33A and 33B illustrate a non-limiting example expanding upon theconstruction of paddle 2502 a of FIG. 25.

As shown, the device 3300 includes the paddle 2502 a of FIG. 25 with theaddition of a bolus 3302. The bolus 3302 may be formed of any suitablematerial to provide desired impedance matching when the paddle 2502 a isbrought into contact with a subject to be imaged. For example, if thesubject is a human patient, the bolus 3302 may include a material havingsubstantially the same impedance as that of human tissue. The bolus 3302may include an outer bag filled with a gel, liquid, or other suitablematerial, and may be attached or otherwise coupled to the paddle 2502 ain any suitable manner In some embodiments, the bolus may not beattached to the paddle, but may be positioned between the subject andthe arrangement of ultrasound elements in any suitable manner.

According to some embodiments of the present application, an apparatusfor performing HIFU is provided. The apparatus may comprise anarrangement of ultrasound elements configured to operate as HIFUelements, and which in some non-limiting embodiments may be arranged (ordistributed) among ultrasound elements configured to operate asultrasound imaging elements. In this manner, a single apparatus mayperform both HIFU and ultrasound imaging, and therefore may beconsidered a dual- or multi-modal apparatus.

In some embodiments in which an apparatus is provided including bothultrasound imaging elements and HIFU elements, one or more of theimaging and HIFU elements may be the same as each other. However, inalternative embodiments, the two types of elements may differ. Forexample, the center frequency, bandwidth, size and/or powerspecifications may differ for the ultrasound elements configured asimaging elements as compared to those configured as HIFU elements. Thetypes of waveforms transmitted may also differ between the differenttypes of elements. In some embodiments, the ultrasound elementsconfigured as imaging elements may be coupled to different types ofcircuitry than those configured as HIFU elements.

HIFU elements, as used herein, are ultrasound elements which may be usedto induce a temperature change in a subject. The temperature change maybe up to approximately 30 degrees Celsius or more, and may be sufficientin some embodiments to cauterize tissue. However, HIFU elements need notachieve cauterization. For example, less energy than that required forcauterization may be applied. In some embodiments, HIFU elements may beused to achieve heat shock or cause apoptosis (programmed cell death).Achieving such results typically requires less energy than that requiredto achieve cauterization, but may still be useful in some embodiments.Typically, HIFU elements deposit more power in a subject thanconventional ultrasound imaging elements.

According to an embodiment, an apparatus may be provided comprising afirst plurality of ultrasound imaging elements and a first plurality ofhigh intensity focused ultrasound (HIFU) elements. The first pluralityof ultrasound imaging elements and the first plurality of HIFU elementsmay be physically coupled to a first support. At least some elements ofthe first plurality of ultrasound imaging elements are disposed among atleast some elements of the first plurality of HIFU elements. Asdescribed, the relative arrangement of ultrasound elements configured asHIFU elements and those configured as ultrasound imaging elements maytake any of various suitable forms.

According to an embodiment, the ultrasound elements configured as HIFUelements may be interspersed (placed at intervals) among the ultrasoundelements configured as imaging elements. The ultrasound elementsconfigured as HIFU elements may be interspersed in a patterned orsubstantially non-patterned manner As a non-limiting example, theultrasound elements configured as HIFU elements may, in combination withthe ultrasound elements configured as imaging elements, form acheckerboard pattern, a non-limiting example of which is described belowin connection with FIG. 34B.

According to an embodiment, the ultrasound elements configured as HIFUelements may be arranged between ultrasound elements configured asimaging elements. For example, referring to FIG. 34A, which illustratesan apparatus 3400 comprising elements configured as HIFU elements 3402and elements configured as imaging elements 3404, one or more of theHIFU elements 3402 may be between two or more of the imaging element3404. In the embodiment shown, the HIFU elements are larger than theimaging elements, but the present aspect is not limited in this respect.

According to an embodiment, the ultrasound elements configured as HIFUelements may be interleaved with (i.e., arranged in an alternatingmanner) the ultrasound elements configured as imaging elements. Theconfiguration of FIG. 34A illustrates a non-limiting example. In theillustrated device 3400, the HIFU elements 3402 are arranged in rowsinterleaved with rows of imaging elements 3404. Alternatively, it may beconsidered that in the illustrated device 3400 the HIFU elements 3402are arranged in columns interleaved with columns of the imaging elements3404.

FIG. 34B illustrates an alternative configuration to that of FIG. 34A inwhich apparatus 3410 comprises the elements configured as HIFU elements3402 and the elements configured as imaging elements 3404 arranged in acheckerboard pattern. Further alternative layouts are also possible.

In embodiments in which ultrasound elements configured as imagingelements (e.g., in an imaging array) are used in combination withultrasound elements configured as HIFU elements (e.g., in a HIFU array),the arrangements of elements may take any suitable spacing. For example,the arrangements of ultrasound elements configured as imaging elementsmay be a sparse arrangement. Additionally or alternatively, thearrangement of ultrasound elements configured as HIFU elements may be asparse arrangement. In some embodiments, the arrangement of ultrasoundelements configured as imaging elements may be a sparse arrangement,while the arrangement of ultrasound elements configured as HIFU elementsmay not be sparse (i.e., may be densely positioned with respect to eachother).

Configurations combining ultrasound elements configured as imagingelements with those configured as HIFU elements may also utilizesubarrays of elements configured as one type or another. FIG. 35Aillustrates a non-limiting example. As shown, the configuration 3500includes subarrays 3504 of ultrasound elements configured as HIFUelements disposed among ultrasound elements configured as ultrasoundimaging elements 3502.

FIG. 35B illustrates an alternative using subarrays of ultrasoundelements configured as imaging elements disposed among ultrasoundelements configured as HIFU elements. Namely, the configuration 3510illustrates subarrays 3512 of ultrasound elements configured as imagingelements disposed among ultrasound elements 3514 configured as HIFUelements.

FIG. 35C illustrates a further embodiment in which subarrays ofultrasound elements configured as imaging elements are disposed amongsubarrays of ultrasound elements configured as HIFU elements. Namely,the configured 3520 illustrates subarrays 3522 of ultrasound elementsconfigured as imaging elements disposed among subarrays 3524 ofultrasound elements configured as HIFU elements. Variations on theillustrated configuration are possible, for example regarding theuniformity of spacing between subarrays and the number of elements ineach subarray, as examples.

According to some embodiments, an array of ultrasound elementsconfigured as HIFU elements may be disposed relative to an array ofultrasound elements configured as imaging elements such that the twoarrays are substantially distinct. FIGS. 35D-35G illustrate non-limitingembodiments. In FIG. 35D, an array 3532 of ultrasound elementsconfigured as imaging elements is disposed next to an array 3534 ofultrasound elements configured as HIFU elements. Here, the array 3532 isto the left of array 3534.

FIG. 35E illustrates a similar configuration utilizing an array 3542 ofultrasound elements configured as imaging elements disposed next to anarray 3544 of ultrasound elements configured as HIFU elements. Here, thearray 3542 is to the right of the array 3544.

FIG. 35F illustrates a further alternative embodiment in which an array3552 of ultrasound elements configured as ultrasound imaging elements ispositioned above an array 3554 of ultrasound elements configured as HIFUelements.

FIG. 35G illustrates a further embodiment in which an array 3562 ofultrasound elements configured as imaging elements is positioned belowan array 3564 of ultrasound elements configured as HIFU elements.

In those embodiments in which an array of ultrasound elements configuredas imaging elements is used in combination with an array of ultrasoundelements configured as HIFU elements, the arrays may have anyorientation with respect to each other. For example, in someembodiments, the arrays may be in the same plane as each other (e.g.,FIGS. 35D-35G). However, in alternative embodiments, the arrays may beoriented at an angle with respect to each other. FIGS. 35H and 351illustrate non-limiting examples.

In FIG. 35H, an array 3572 of ultrasound elements configured as imagingelements is angled relative to an array 3574 of ultrasound elementsconfigured as HIFU elements by an angle α. The angle may be ninetydegrees (a right angle) or less than ninety degrees. In FIG. 351, anarray 3582 of ultrasound elements configured as imaging element may alsobe angled relative to an array 3584 of ultrasound elements configured asHIFU elements, with the angle a being greater than ninety degrees.

In some embodiments in which one or more arrays of ultrasound elementsconfigured as imaging elements are used in combination with one or morearrays of ultrasound elements configured as HIFU elements (e.g., theembodiments of FIGS. 35D-35I), the arrays of imaging elements may beseparate from the arrays of HIFU elements. For example, the arrays ofimaging elements may be formed on a separate substrate from the arraysof HIFU elements, may be movable independent of the arrays of imagingelements, and may be electrically separated (e.g., separate powersupplies, separate communication inputs and outputs, etc.). However, insome embodiments, arrays of imaging elements may be disposed on the samesubstrate as arrays of HIFU elements and/or may share electronics and/ormay be movable together as a unified entity. In some such embodiments,the substrate may be acoustically insulating, and thus formed of anysuitable acoustically insulating material.

FIGS. 36A and 36B illustrate examples alternative subarrayconfigurations to that of the rectangular subarrays of FIG. 35. As shownin FIG. 36A, the subarrays 3600 a of ultrasound elements configured asHIFU elements may have a trigonal structure. FIG. 36B illustrates afurther alternative, in which the subarrays 3600 b may have a hexagonalstructure. Further alternatives are possible.

In any of the foregoing embodiments in which a device includesultrasound elements configured as HIFU elements and ultrasound elementsconfigured as imaging elements, the elements may be in a fixed relationwith respect to each other. Maintaining such a fixed relation mayfacilitate processing of imaging data and control over a location atwhich HIFU is performed relative to the imaged subject. Even so, itshould be appreciated that the elements may be placed on a flexiblesubstrate (e.g., of the types previously described with respect to FIG.28) and maintain suitable operation.

It should be appreciated that the embodiments illustrated and describedabove in which configurations of ultrasound elements includes thoseconfigured as HIFU elements in addition to those configured as imagingelements may have any suitable spacing of elements. For example, theelements configured as HIFU elements may be spaced at any suitabledistances from elements configured as imaging elements. According to anembodiment, the pitch between HIFU elements may be approximately thesame as the pitch between imaging elements. For example, the pitchbetween both types of elements may be between approximately 2 mm and 10mm (e.g., 3 mm, 5 mm, etc.). Moreover, one or both types of elements mayhave a regular spacing, irregular spacing, or random spacing, accordingto various embodiments. As described previously, utilizing a sparsearrangement of ultrasound elements configured as imaging elements mayfacilitate accommodation of ultrasound elements configured as HIFUelements within the illustrated configurations. Namely, the ability toperform ultrasound imaging utilizing a sparse array of ultrasoundelements may allow for ultrasound elements configured as HIFU elementsto be positioned among (e.g., disposed between, interspersed with,interleaved with, etc.) the ultrasound elements configured as ultrasoundimaging elements.

According to an aspect of the present application, one or both of thearrangements of HIFU elements and imaging elements may be sparse. Itshould be appreciated that sparsity may be different for the two typesof arrangements since sparsity may relate to a frequency of operationand, as described previously, the frequencies of operation of theimaging elements may differ from those of the HIFU elements. Thus, itshould be appreciated that the pitch of the two types of elements may bethe same even though only one of the two types may be arranged sparsely,according to a non-limiting embodiment.

FIGS. 37 and 38 illustrate further non-limiting examples of suitableconfigurations implementing ultrasound elements configured as HIFUelements in addition to ultrasound elements configured as imagingelements. In FIG. 37, the configuration 3700 includes ultrasoundelements configured as imaging elements 3702 and ultrasound elementsconfigured as HIFU elements 3704. In FIG. 38, the configuration 3800includes ultrasound elements configured as imaging elements 3802 andultrasound elements configured as HIFU elements 3804.

In those embodiments in which arrays or subarrays of ultrasound elementsconfigured as HIFU elements are used, the arrays or subarrays mayexhibit any one or more of the characteristics of arrangements ofultrasound imaging elements described herein. For example, in someembodiments, sparse arrays of ultrasound elements configured as HIFUelements may be used. In some embodiments, irregular arrangements ofultrasound elements configured as HIFU elements may be used.

In some embodiments, arrangements of ultrasound elements configured asimaging elements and/or HIFU elements may be operated in a manner toprovide a desired effective arrangement. For example, a denselypopulated arrangement of ultrasound elements configured as imagingelements may be operated as a sparse arrangement by activating only asuitable subset of the elements. The same may be true for arrangementsof HIFU elements. In the same manner, subsets of an arrangement may beoperated in a manner to provide an effective irregular arrangement(whether for imaging or HIFU). More generally, embodiments according tothe present application provide for operation of subsets of arrangementsof radiation elements to provide desired characteristics of thearrangements, such as any of those characteristics described herein.

Those aspects of the present application in which HIFU is performed mayprovide for focusing of the HIFU signal (or beam) in any suitable mannerThus, beamforming may be performed, in any of the manners previouslydescribed herein with respect to imaging or in any other suitable mannerIn some embodiments, time reversal beamforming may be used. Also, anysuitable type of beam (e.g., a pencil beam, a fan beam, etc.) may beformed. The type of beam formed may depend, in some embodiments, on thegeometry of the HIFU configuration. For example, depending on the shapeof the subject being targeted with HIFU and the configuration ofultrasound elements, a particular beam type may be chosen.

According to an aspect, the HIFU beam may be focused by suitableexcitation of the HIFU elements of a device, and thus any such devicemay be referred to as an electronically scanned HIFU array, to bedistinguished from geometric focusing systems. Moreover, any desireddepth of focus may be provided. In some embodiments, a HIFU focal lengthmay be movable in two or three dimensions, for example by suitableexcitation of HIFU elements. In some embodiments, the device(s) may be anear field HIFU device. The larger the arrangement of HIFU elements, thegreater the depth of focus which may be provided. Moreover, it should beappreciated that devices according to the aspects described herein inwhich HIFU elements are used may provide the capability to focus theHIFU beam in three dimensions (e.g., in x, y, and z-directions). Thus,precise control over location of HIFU deposition may be provided. Insome embodiments, one or more HIFU elements may be located on one of thearrays (e.g., array 102 a). In some embodiments, one or more HIFUelements may be located on each of the arrays (e.g., arrays 102 a and102 b).

Also, according to an embodiment, ultrasound elements of an arrangementmay be configured to exhibit time-varying operation as HIFU elements orimaging elements. For example, referring to the configuration 3700 ofFIG. 37, the ultrasound elements 3702 may be configured to operate asimaging elements during a first time period and as HIFU elements duringa second time period. Similarly, the behavior of elements 3704 mayalternate between functioning as HIFU elements and imaging elements.

The various aspects described herein relating to configurations ofultrasound elements including those configured as HIFU elements andthose configured as imaging elements are not limited to two-dimensional(2D) arrangements. Rather, the elements configured as HIFU elements maybe arranged in two or more dimensions and/or the elements configured asimaging elements may be arranged in two or more dimensions. In someembodiments, the HIFU elements may be coplanar and/or the imagingelements may be coplanar. Again, though, not all embodiments are limitedin this respect.

According to an aspect of the present application, an apparatuscomprising ultrasound elements configured as HIFU elements andultrasound elements configured as imaging elements is configured suchthat the two types of elements operate at different frequencies. Thus,HIFU and imaging may be provided at the same time, without the imagingfunctionality being negatively impacted by the HIFU. The elementsconfigured as HIFU elements may be configured to operate in a firstfrequency range while the elements configured as imaging elements may beconfigured to operate in a second frequency range. The first and secondfrequency ranges may be entirely distinct (e.g., being separated by atleast 3 MHz, at least 5 MHz, or any other suitable frequencyseparation), or may have some overlap in some embodiments. Asnon-limiting examples, the elements configured as HIFU elements may beconfigured to operate in a range from approximately 100 KHz-5 MHz, whilethe elements configured as imaging elements may be configured to operatein a range from approximately 1-40 MHz Other ranges are also possible.

Furthermore, in some embodiments, an array of ultrasound elementsconfigured as HIFU elements may include ultrasound elements operating atdifferent frequencies. For example, a HIFU array may include one or moreHIFU elements configured to operate at a first frequency and one or moreHIFU elements configured to operate at a second frequency. The first andsecond frequencies may take any suitable values and may have anysuitable relationship with respect to each other.

In those embodiments in which a device comprises ultrasound elementsconfigured as imaging elements in addition to those configured as HIFUelements, the elements may be physically supported in any suitablemanner For example, according to an embodiment, the elements configuredas HIFU elements and those configured as imaging elements may be coupledto a common support (e.g., of the type shown in FIG. 25 or any othersuitable type). Alternatively, the two types of elements may be coupledto distinct supports, which themselves may be coupled together.

According to an embodiment, an arrangement of HIFU elements and imagingelements may be formed into an apparatus which may be handheld. Forexample, a paddle of the type shown in FIG. 25 may be implemented, withthe addition of elements configured as HIFU elements. Moreover, multiplesuch apparatus may be provided. Thus, according to an embodiment, twopaddles may be provided, one or both of which may include HIFU elementsand imaging elements. A non-limiting example is illustrated in FIG. 39.

The apparatus 3900 includes several of the components previouslyillustrated and described with respect to FIG. 27. However, the paddles3902 a and 3902 b both include ultrasound elements configured as imagingelements and ultrasound elements configured as HIFU elements. As anon-limiting example, paddles 3902 a and 3902 b may include respectivearrangements 3904 a and 3904 b of the type previously illustrated inFIG. 34A including HIFU elements 3402 and imaging elements 3404. Otherconfigurations of imaging elements and HIFU elements are also possible.In some embodiments, for either or both of the paddles, the HIFUelements and imaging elements may be in a substantially fixedrelationship with respect to each other. In some embodiments, thepaddles may include flexible supports, for example as previouslydescribed herein.

Transmissive ultrasound imaging may be performed using the twoarrangements of ultrasound elements configured as imaging elements, inthe manner previously described herein. Additionally, or alternatively,both paddles (e.g., paddles 3902 a and 3902 b) may provide HIFUfunctionality, thus allowing for HIFU to be directed at a subject frommultiple angles (e.g., from opposing sides of the subject). Suchoperation may allow for each of the HIFU arrangements individually touse less power (e.g., approximately half the amount of power) to achievethe same HIFU operation as would be needed if only a single arrangementof HIFU was used.

Thus, it should be appreciated by reference to, for example, FIGS. 34A,34B, and 39 (among others), that embodiments of the present applicationprovides an apparatus comprising a support, a first plurality ofultrasound elements configured as ultrasound imaging elements, and asecond plurality of ultrasound elements configured as high intensityfocused ultrasound (HIFU) elements. The first plurality and secondplurality of ultrasound elements may be physically coupled to the firstsupport, and at least some elements of the first plurality of ultrasoundelements are arranged among at least some elements of the secondplurality of ultrasound elements. In some such embodiments, two or moresuch apparatus may be provided (e.g., two paddles of the typesillustrated in FIG. 39). In some embodiments, each of the firstplurality of ultrasound imaging elements is configured to perform atleast one of emission of a radiation source signal incident upon avolume to be imaged three-dimensionally or detection of such a radiationsource signal.

In those embodiments in which multiple arrangements of imaging elementsare provided with one or more arrangements of HIFU elements, therelative orientation and/or position of the arrangements (e.g., of theimaging arrangements with respect to each other) may be determined tofacilitate combined operation. For example, the relative orientationand/or position may be determined in any manner previously describedherein, such as those described with respect to FIG. 27.

According to an aspect of the present application, an apparatus of thetypes described herein may be used to perform thermometry. Temperaturemeasurements may be based on several types of data. According to someembodiments, the speed of sound in a material (e.g., human tissue) maydepend on the temperature of the tissue. As has been describedpreviously, the speed of sound in a subject may be determined usingvarious aspects described herein (e.g., the apparatus of FIGS. 1-6, asnon-limiting examples). For example, by detecting changes in the speedof sound through a subject, changes in temperature of the subject may bedetermined. As another example, by detecting the speed of sound at alocation within a subject being imaged, the temperature at the locationmay be determined.

According to an embodiment, thermometry may be performed based on theindex of refraction of a subject. Thus, using any of the systemsdescribed herein suitable for detecting index of refraction of a subjectmay be used to also determine temperature of the subject using anysuitable processing techniques.

According to another embodiment, TOF data collected by ultrasoundsource-sensor pairs may provide an indication of temperature of asubject. Thus, as an example, operation of a system like that of FIG. 4,5 or 6 may be used to collect TOF data. The TOF data may be processedusing any suitable techniques to determine temperature of the subject.

In some embodiments, raw waveforms collected by ultrasound sensorsoperating in combination with ultrasound sources in a transmissivemodality may be analyzed for changes (e.g., changes in amplitude, phase,etc.). Such changes may be indicative of changes in temperature of asubject. Thus, for example, systems like those in FIGS. 4, 5 and 6 maybe used to collect raw waveforms which may be processed using anysuitable techniques to determine temperature of a subject.

In those embodiments in which raw waveforms are used to detect changesin temperature, principles of coherence may be utilized. For instance,in some embodiments a change in temperature may be detected when awaveform de-coheres from its previous form. Waveforms representing soundspeed and attenuation may be analyzed individually or in combination forsuch de-coherence. According to some embodiments, coherence of the rawwaveform of a chirp may be analyzed and any de-coherence in the receivedchirp waveform may be used to determine a change in temperature of thesubject. In some embodiments, absolute temperature may also bedetermined in addition to or as an alternative to temperature changes.

According to an embodiment of the present application, athree-dimensional (3D) temperature profile may be constructed based atleast partially on data collected using apparatus of type describedherein. Temperature values or changes in temperature may be determinedin any of the manners described herein. In some embodiments, atemperature value or change in temperature may be determined for aplurality of voxels corresponding to a volume to be characterized (e.g.,subject 410 of FIG. 4). The temperature-related values of the voxels maytherefore be used to construct a temperature profile of the volume.Because the voxels may be arranged in three-dimensions in someembodiments, a 3D temperature profile of the volume may be constructed.FIG. 40 illustrates a non-limiting example.

The temperature profile 4002 includes a plurality of temperature-relatedvalues corresponding to voxels 4004 associated with the subject ofinterest. In this non-limiting embodiment, the temperature-relatedvalues represent absolute temperature in degrees Fahrenheit. The profilemay be displayed or otherwise presented to a user in any suitablemanner, including via a 2D display, a 3D display, or in any othersuitable manner.

The performance of thermometry may be combined with other operationsdescribed herein. For example, according to an embodiment, an apparatusmay be configured as a multi-mode apparatus to perform ultrasoundimaging, HIFU, and thermometry, or any combination of those functions.The performance of thermometry may be used in combination with HIFU tomonitor the temperature of a subject undergoing HIFU treatment, as anon-limiting example.

In some embodiments, thermometry may be used for classifying an imagedsubject. For example, tissue type may be determined based, at leastpartially, on the temperature behavior of the tissue. Other thermalclassification is also possible.

As previously mentioned, in some embodiments, a volumetric image orimages generated according to any of the previously-described techniques(e.g., the techniques described with reference to FIG. 29), may beoutput to a viewer (e.g., a doctor) for viewing and/or manipulation.Volumetric image(s) may be output to the viewer in any suitable way. Insome embodiments, volumetric image(s) may be output to the viewer via aconventional two-dimensional display of a computing device (e.g., thescreen of a computer monitor). The viewer may view the image(s) on thetwo-dimensional display and manipulate the image(s) on the computerscreen by using a mouse, a touch screen, or a keyboard. However, in someembodiments, described in greater detail below, a user interface may usea three-dimensional (3D) display configured to present a volumetricimage or images to the viewer in three-dimensional (3D) space.Additionally, the user interface may allow the viewer to manipulate apresented volumetric image in 3D space. In some embodiments, suchmanipulation may be performed by the user via a controller (e.g., awired or wireless stylus, a wired or wireless remote control, a wired orwireless mouse, an inertial navigation system (e.g., 3-axisaccelerometer and/or 3-axis gyroscope) or with motion (e.g., handmotion).

The inventors have appreciated that various benefits may be achieved byutilizing a user interface configured to present volumetric images to aviewer via a 3D display and, optionally, allow the viewer to manipulatethe presented images in three dimensions. For example, a doctor viewingsuch images via a 3D display may view a 3D image corresponding to anorgan (or a subsection of the 3D image corresponding to a portion of theorgan), enlarge it, shrink it, tilt it, rotate it, and/or manipulate itin any other suitable way to help diagnose a patient and/or plan asurgical path for applying HIFU to the organ, for performing othersurgical procedures, or simply to alter viewing conditions of the image.The user may want to view only a portion of an image, or multipleportions in sequence, and may be able to do so by a suitableuser-selection tool (e.g., an option on a computer user interface, amouse, etc.).

Illustrative embodiments of the operation of a user interface configuredto present one or more volumetric images to a viewer via a 3D displayare described below with reference to FIG. 41, which is a flow chart ofprocess 4100. Process 4100 may be performed by any suitable hardwareand, for example, may be performed, at least in part, by using system400 (as a non-limiting example), previously described with reference toFIG. 4. In some embodiments, one or more hardware components of thesystem may be configured to implement a three-dimensional display and/orto receive input from a user as described in greater detail below.

Process 4100 begins at act 4102, where one or more volumetric images ofa subject being imaged may be obtained. The volumetric image(s) may beobtained in any suitable way. In some embodiments, the volumetricimage(s) may be accessed after having been obtained by using an imagingdevice and made available for subsequent access (e.g., by storing theimage(s) on at least one non-transitory computer-readable storagemedium) during act 4102. Additionally or alternatively, the volumetricimage(s) may be obtained by using an imaging device as part of act 4102.

The volumetric image(s) may be obtained by any suitable imaging devicein any suitable way. For example, the volumetric image(s) may beobtained by collecting imaging related data using an imaging devicecomprising arrays of sources and sensors in any suitable way (e.g.,using an ultrasound imaging device operating in a transmissivemodality), examples of which were previously described with reference toprocess 2900 in FIG. 29. Each volumetric image obtained at act 4102 maybe of any suitable type and may comprise one or more values of thecorresponding type for each voxel in the volumetric image. Examples ofvolumetric images that may be obtained include, but are not limited to,volumetric images comprising for each voxel (or each of two or morevoxels, but not necessarily all voxels in some embodiments) one or moretime-of-flight values, one or more attenuation values, one or more speedof sound values, one or more index of refraction values, one or morescattering potential values, one or more absorption values, one or moretemperature values, one or more values indicative of energy power beingapplied to the voxel, one or more susceptibility values, one or moreDoppler values, one or more spectral attenuation values, one or morevalues obtained via a two-pulse coherent change detection technique, oneor more values obtained via a two-pulse incoherent change detectiontechnique, one or more values obtained via an elastography technique, orany other suitable types of values. Any number of images may beobtained, and they need not all represent the same type of data. As aspecific non-limiting example, two volumetric images may be obtained atact 4102 with the first volumetric image comprising one or more index ofrefraction values for each voxel and the second volumetric imagecomprising one or more temperature values for each voxel in the image.Though, it should be appreciated that any suitable number of volumetricimages of any suitable type may be obtained.

In some embodiments, other data comprising measurements of the subjectbeing imaged may be obtained in addition to one or more volumetricimages. Examples of such data include, but are not limited to,electrocardiogram (ECG/EKG) data, electroencephalography (EEG) data,blood pressure data, and any other suitable data comprising measurementsof the subject being imaged.

After one or more volumetric images of the subject being imaged areobtained, process 4100 proceeds to act 4104, where, if multiplevolumetric images were obtained at act 4102, the volumetric images arecombined to form a single fused volumetric image so that the singlefused volumetric image may be subsequently presented to the viewer via a3D display. If only one volumetric image was obtained at act 4102, thenprocess 4102 simply proceeds to act 4106, but for ease of explanationsuch a volumetric image is also referred to as a fused volumetric imagein the remainder of the description of process 4100.

Volumetric images may be fused in any suitable way. In some embodiments,volumetric images may be fused at a voxel level by associating a uniquevisual cue to each of the values in the fused image that originate froma single volumetric image obtained at act 4102. Any suitable type ofvisual cue may be used including, but not limited to, color,transparency, and/or shading. When the fused volumetric image issubsequently displayed via the 3D display, the visual cues may help theviewer compare various aspects of the subject being imaged on the sameimage.

As a non-limiting illustrative example, a volumetric image comprising anindex of refraction value for each voxel and a volumetric imagecomprising a temperature value for each voxel may be used to construct afused volumetric image in which each voxel may be associated with anindex of refraction value and/or a temperature value, as well as onevisual cue (e.g., one color map mapping values to colors) associatedwith the index of refraction values and a different visual cue (anothercolor map mapping values to colors in a different way) associated withthe temperature values. Accordingly, when the fused image issubsequently displayed via the 3D display, the visual cues may help theviewer compare various aspects of the subject being imaged (e.g., indexof refraction vs. temperature) on the same image. In some embodiments, avoxel may be displayed by using a mixture of the colors associated withthe voxel.

Next, process 4100 proceeds to act 4106, where one or more imageanalysis techniques may be applied to the fused volumetric image. Imageanalysis techniques may be applied to obtain image features that may, insome embodiments, be used to automatically detect one or more problems(e.g., an area of diseased tissue) in the subject being imaged, and/orautomatically identify the types of problem(s) detected (e.g., thedetected area of diseased tissue is cancer).

In some embodiments, image analysis techniques may be applied to thefused volumetric image to automatically identify at least one shape inthe fused volumetric image. The image analysis techniques may be used toobtain information about the one or more identified shapes in the fusedvolumetric image. The obtained shape information may, in turn, be usedto automatically detect and classify problems in the subject beingimaged. Information about a shape may comprise information about thesize of the shape, volume of the shape, orientation of the shape,density of a volume bound by the shape, crinkliness of an object, andone or more values representing the shape itself. For example, the shapemay be represented by multiple coefficients in a three-dimensional basis(e.g., spherical harmonic coefficients, wavelet coefficients, etc.) andinformation about the shape may include such coefficients.

In some embodiments, features obtained from the fused volumetric image(including, but not limited to, information about one or more shapes inthe image) may be used to automatically detect and classify one or moreproblems in the subject being imaged, to categorize the imaged subject(e.g., as a particular type of subject, as a particular type of tissue,etc.), or may be used for any other desired purpose. For example, thefeatures may be used to automatically detect the presence of cancer,kidney stones, cysts, fluid-filled cavities, foreign objects, brokenbones, or any other problems within the body. The detection andclassification of problems in the subject being imaged based on one ormore features obtained from the fused volumetric image may be done inany suitable way using any suitable techniques and tools including, butnot limited to, machine learning techniques (classifiers, Bayesiannetworks, support vector machines, neural networks, decision trees,hidden Markov models, graphical models, clustering (e.g., binning orhistograms as examples), etc.), statistical inference (e.g., Bayesianinference, maximum likelihood estimation, etc.), and tracking techniques(target tracking, scene tracking, volume tracking, etc.). In thoseembodiments in which images are analyzed to categorize or classify theimaged subject, such categorization or classification may be performedin any suitable manner In some embodiments, an image of a subject may becompared against a template image (or, more generally, template data) toaid the classification or categorization.

In some embodiments, the fused volumetric image may be updated to showany of the information obtained as part of act 4106. For example, thefused volumetric image may be updated to show one or more identifiedshapes, when displayed. As another example, the fused volumetric imagemay be updated to indicate how a shape or an area of the subject beingimaged was classified, when displayed.

After image analysis techniques are applied at act 4106, process 4100proceeds to act 4108, where viewer input, at least partially specifyinghow the fused volumetric image is to be presented to the viewer, isreceived. The viewer input may specify a position where the fusedvolumetric image is to be displayed, an orientation for the displayedimage, and a size for the displayed image. Additionally oralternatively, the viewer input may identify a portion of the image tobe displayed to the viewer. The viewer may provide these and/or anyother suitable inputs in any suitable way including, but not limited to,by using a stylus pen, a mouse pad, a keyboard, a remote control, and/ora detection mechanism configured to detect movements of the viewer(e.g., leg movements, arm movements, hand movements, finger movements,eye movements, etc.) suggestive of the viewer's desired presentation ofthe image. A non-limiting example of such 3D detection mechanisms is theLeap device, available from Leap Motion of San Francisco, Calif. Suchtechnology may allow the viewer to control the image by pointing,waving, and/or using other natural gestures (e.g., hand gestures) withina detection space monitored by the Leap device.

Next, the process 4100 proceeds to act 4110, where the fused volumetricimage obtained in acts 4102-4106 is further processed to prepare thefused volumetric image for subsequent presentation to the viewer via a3D display. This may be done in any suitable way. In some embodiments, astereoscopic conversion algorithm may be applied to the fused volumetricimage to produce two stereoscopic images, each of which will bepresented to a different eye of the viewer via the 3D display. Thestereoscopic conversion algorithm may produce the two stereoscopicimages based at least in part on the viewer input provided at act 4108.

Next, process 4100 proceeds to act 4112, where the images produced bythe stereoscopic conversion process are presented to the viewer via the3D display. This is illustrated in FIG. 42, which illustrates displayingimages 4202 (Image A) and 4204 (Image B) obtained from a fusedvolumetric image to the viewer by displaying the image 4202 onto eye4206 and image 4204 onto eye 4208. Images A and B may be 2D projectionsin some embodiments, representing a rendering of a scene from twodifferent perspectives.

Any suitable type of 3D display may be used to present the images to theuser. For example, in some embodiments, a 3D display such as the zSpacedisplay available from Infinite Z, Inc.® may be used. In otherembodiments, any suitable lenticular display may be used. In otherembodiments, “active” 3D technologies may be used which provide a 3Ddisplay at least in part by actively switching shutters on the left andright eye. In other embodiments, the images may be presented as red/blueimages to a user wearing “3D glasses,” presented as polarized imageshaving different polarizations, presented as time-gated alternatingimages, or may be presented in any other suitable way. In someembodiments, a 3D display may be a heads-up display similar to thedisplays presented to pilots operating aircraft. In some embodiments,additional information about the subject being imaged (e.g., ECGinformation obtained at act 4102) may be presented to the viewer as partof the image or concurrently with the image.

Next, process 4100 proceeds to decision block 4114, where it isdetermined whether additional viewer input is received. Such input maybe any input provided by the viewer to specify an update to how thefused volumetric image is displayed to the viewer. For example, theinput may specify to update the fused volumetric image by rotating theimage, shrinking the image, enlarging the image, viewing one or moredesired portions of the image, mapping the underlying data of the imageto a new coordinate system, etc.). A non-limiting example is illustratedin FIG. 43.

The system 4300 allows a user 4302 to view a 3D image 4306 (e.g.,produced at act 4112 in FIG. 41), for example by wearing 3D glasses 4304or in any other suitable manner The 3D image may be generated by a 3Ddisplay device 4308. The user may use a device 4310 (e.g., a stylus penor other device) to manipulate the 3D image 4306 or to otherwise provideinput (e.g., identifying a point of interest in the image).

If it is determined at act 4114 that additional viewer input isprovided, process 4100 returns to acts 4110-4112, where the way in whichthe fused volumetric image is displayed to the viewer, via the 3Ddisplay, is updated. If no such input is provided at act 4114 (e.g.,after a predetermined period of time), process 4100 completes.

It should be appreciated that process 4100 is illustrative and thatvariations of process 4100 are possible. For example, although in theillustrated embodiment a single fused volumetric image is presented tothe user via a 3D display, in other embodiments multiple fusedvolumetric images may be presented to the user via the 3D display. Insuch embodiments, process 4100 may be applied to each of multiple fusedvolumetric images, one or more of which may have been obtained fromvolumetric images taken at different points in time. In some suchembodiments, the multiple fused volumetric images may be displayed tothe user in a time-dependent manner, in real time or in accordance withany other suitable timing. In this manner, a movie of the volumetricimages may be presented. The passage of time may represent a fourthdimension and therefore some embodiments of the present applicationprovide four-dimensional (4D) imaging.

The inventors have appreciated that it may be desirable to presentvolumetric images to a viewer from different points of view, via a 3Ddisplay or any other suitable type of display. Accordingly, in someembodiments, a user interface may be configured to present, to a viewer,any volumetric image from one or more points of view (i.e., from theperspective of a viewer located at the point(s) of view) external to thevolumetric image. This way a volumetric image of a subject being imagedmay be presented to the viewer from any point of view external to oroutside of the subject. For example, a volumetric image of an organ(e.g., heart, kidney, etc.) may be presented to the viewer from anypoint of view external to the organ. Additionally or alternatively, insome embodiments described in more detail below, the user interface maybe configured to present any volumetric image from one or more points ofview within the volumetric image. For example, a volumetric image of abody cavity may be presented to the viewer from any point of view withinthe body cavity. In this respect, the user interface may provide theviewer with the type of images that may be obtained by inserting adevice (e.g., an endoscope, a tube, a needle (e.g., a biopsy needle))inside of the subject being imaged (e.g., inside of a body cavity) tocapture images of the subject from points of view within the subject,but without the need for such a device. Accordingly, such a userinterface may be referred to as a “virtual” endoscope. The user may viewthe imaged subject from points internal to the subject at any desiredangle (e.g., looking up from within the subject, looking down, etc.).Such viewing may be static in some embodiments such that a static imagefrom within the subject is presented. In other embodiments, such viewingmay be dynamic, for example allowing the viewer to see the subject asthe view “travels” along a path through the subject (e.g., as anendoscope or other device might).

Thus, the user interface is not limited to presenting a volumetric imagefrom a single point of view, regardless of whether the point of view iswithin or external to the subject being imaged, and may be configured topresent the volumetric image from multiple points of view. For example,in some embodiments, the user interface may be configured to present thevolumetric image from each of multiple points of view that lie along apath. The path may lie entirely within the subject being imaged (inanalogy to a path a physical endoscope would follow through a body beingimaged), entirely external to the subject being imaged, or at least onepoint on the path may lie inside the subject being imaged and at leastanother point on the path may lie outside of the subject being imaged.

FIG. 44 illustrates a flowchart of process 4400 for displaying one ormore images to a viewer from one or more points of view within thesubject being imaged. Process 4400 may be performed by any suitablehardware and, for example, may be performed, at least in part, by usingsystem 400, previously described with reference to FIG. 4.

Process 4400 begins at act 4402, where one or multiple volumetric imagesof a subject may be obtained for subsequent presentation to the viewerfrom one or multiple points of view within the volumetric image. Thevolumetric image may be obtained in any suitable way and be of anysuitable type, as previously described with reference to act 4102 ofprocess 4100. For example, the volumetric image may be accessed afterhaving been previously obtained.

Next, process 4400 proceeds to decision block 4404, where it may bedetermined whether one or more points of view from which the receivedvolumetric image(s) are to be presented are to be identified manually orautomatically. This determination may be made in any suitable way and,for example, may be made based on input from a user (e.g., a viewer orany other user) indicating whether the user will manually identify thepoint(s) of view. Identifying a point of view may involve identifying alocation within the subject and an angle (or direction) from theidentified location. In some embodiments, multiple points of view (andtherefore multiple locations and angles) may be identified and imagesmay be displayed to a viewer from the multiple points of view, forexample in a time-based sequence as a non-limiting example. In someembodiments, multiple images may be presented to a user corresponding tomultiple points of view in a sequence corresponding to an ordering ofmultiple locations along a path identified by a user or determinedautomatically.

Regardless of how such a determination is made at decision block 4404,when it is determined that a user will manually identify the point(s) ofview, process 4400 proceeds to act 4408, where user input identifyingthe point(s) of view is received. For each identified point of view, theuser input may specify a location of the point of view and/or one ormore viewing angles. A user may provide input to identify the desiredpoints of view in any suitable way. For example, in some embodiments,the user may provide input specifying a path through a volumetric imageobtained at act 4402 using a configuration like that of FIG. 43 (e.g.,by drawing a path in the volumetric image by using a stylus pen, a mousepad, a remote control, and/or a detection mechanism configured to detectmovements of the viewer (examples of which were previously described)).In some embodiments, the user may provide such input while beingpresented with the image. For example, the user may be viewing avolumetric image via a 3D display and draw a path through the displayedvolumetric image by moving a pointing device, a finger, or any othersuitable object along the path the user desires to draw (e.g., as may bedone with the system 4300 of FIG. 43). The path indicated by the motionmay be detected via the aforementioned detection mechanism and providedto the user interface.

On the other hand, when it is determined at decision block 4404 that auser will not specify the point(s) of view manually, process 4400proceeds to act 4406, where the point(s) of view are identifiedautomatically. This may be done in any suitable way. The point(s) ofview may lie along one or more paths through the subject being imagedand the point(s) of view may be identified at least in part byidentifying one or more paths through the subject. For example, in someembodiments, one or more paths through the subject being imaged may beidentified by using image analysis techniques (e.g., computer visiontechniques), examples of which were previously described with referenceto FIG. 41. For instance, image analysis techniques may be applied tothe volumetric image obtained at act 4402 to identify one or morephysical paths in the subject being imaged (e.g., paths througharteries, veins, body cavities, etc. when a human subject is beingimaged). To this end, image analysis techniques including, but notlimited to, image segmentation techniques, shape-fitting techniques,least-squares methods, and tracking techniques may be used.

In some embodiments, a path through the subject being imaged may beidentified using computer vision routines for understanding content ofan image or images of the subject. As an example, features of an imagedsubject, such as boundaries, circular canals or cavities, may beidentified by using segmentation techniques (e.g., based on changes inimage intensity) and then fitting shapes such as ovals in 2Dcross-sectional slices, or fitting piece-wise cylinders and/orellipsoids in 3D volumes. In another embodiment, a least-squaressolution and/or a probabilistic solution to analyzing an image may beused to determine the path. Moreover, a path may be updated in realtime, for example using a tracking technique such as, but not limitedto, Kalman filtering. Other techniques for determining a path are alsopossible.

After at least one point of view (e.g., along a path through avolumetric image) is specified, manually or automatically, process 4400proceeds to act 4410, where multiple images are presented to the viewersuch that each of the images is presented from the identified point(s)of view. In some embodiments, when the points of view lie along a path,the images may be presented to the user sequentially such that thesequence of images presented corresponds to an ordering of the points ofview along the path. In this way, the user may feel as though he isviewing images produced by a moving “virtual” endoscope. Also,presentation of multiple 3D images in this manner may function toeffectively provide 4D imaging of a subject, for example with time(i.e., the passage of time related to traveling along the path) servingas the fourth dimension, and with the images be presented according toany desired timing scheme (e.g., in real time, with a desired timedelay, or in accordance with any other suitable timing scheme). Thus, itshould be appreciated that in some embodiments real time display of 3Dreal time imagery may be provided.

The images may be presented using any suitable display including any ofthe previously-described 3D displays. Images of a path through a subjectmay be displayed together with volumetric images of the subject in someembodiments.

In some embodiments, the viewer may manipulate any of the presentedimages. For example, for each image, the viewer may change the point ofview for the image (e.g., by providing input to pan and tilt the image,move the image from side to side, and/or up and down).

In some embodiments, images produced at act 4410 may be displayed to oneor more remote users (e.g., over the Internet and/or any other suitablenetwork). Such functionality may be desirable in numerous types ofapplications such as telemedicine. For example, a doctor locatedremotely from an operating room in which a medical procedure is takingplace and in which the subject of the medical procedure is being imagedmay be able to view the images and provide input to a surgeon (or otherpersonnel) or a device (e.g., a surgical robot) performing the medicalprocedure.

The inventors have further appreciated that it may be desirable not onlyto present a viewer with images of a subject being imaged from multiplepoints of view that lie along a path, at least partially intersectingthe subject, but also to apply HIFU along the path. The purpose of theHIFU may be to heat tissue along the path, cauterize tissue along thepath, ablate tissue along the path, and/or for any other suitablepurpose.

Accordingly, in some embodiments, a path at least partially intersectingthe subject being imaged may be identified and HIFU may be applied tothe subject along one or more points in the path. This may be done inany suitable way, an illustrative example of which is described belowwith reference to FIG. 45, which shows illustrative process 4500 foridentifying a path at least partially intersecting a subject beingimaged and applying HIFU along the path. Process 4500 may be performedby any suitable system configured to image a subject and apply HIFU tothe subject, an example of which is system 400 described with referenceto FIG. 4.

Process 4500 begins at act 4502, where a target area in the subjectbeing imaged is identified for subsequent treatment by the applicationof at least one HIFU beam. This may be done in any suitable way. Forexample, the target area may be identified automatically by using imageanalysis algorithms, examples of which were previously described withreference to FIG. 41. Alternatively, the target area may be identifiedmanually by a user providing any suitable type of input, examples ofwhich were previously described with reference to act 4408 of FIG. 44.In some embodiments, the target area may be identified by a user viewingan image of the subject (e.g., any of the types of images previouslydescribed herein) and identifying the target area from the image. Forexample, the user may view a 3D image of a subject, manipulate the image(e.g., rotate the image, enlarge the image, etc.) and thereby locate thetarget area within the image. Regardless of how a target area isidentified, the target area may be any suitable type of target area. Forexample, in medical applications, the target area may comprise tissuethat is to be treated or destroyed by the application of HIFU.

After the target area is identified, the process 4500 proceeds to act4504, where one or more target points in the target area are identified.In some embodiments, the target points may lie along a path at leastpartially intersecting the target area. The identified path may be usedto determine how HIFU is to be applied to the target area identified atact 4502. The path at least partially intersecting the target area maybe identified in any suitable way. In some embodiments, the path may beidentified automatically, for example, by using techniques describedwith reference to act 4406 and FIG. 44. In other embodiments, the pathmay be identified based, at least in part, on input from a user, forexample, as previously described with reference to act 4408 and FIG. 44.For example, the user may specify a path at least partially intersectingthe target area, while viewing a volumetric image of the target area(using a 3D display or any other suitable type of display), by drawing apath through the displayed target by moving a pointing device, a finger,or any other suitable object. The path indicated by the motion may bedetected via the aforementioned detection mechanism and used to providethe specified path to the system executing process 4500.

In some embodiments, after the target point(s) have been specified, thesystem executing process 4500 may display the target point(s) togetherwith the target area (e.g., by overlaying a path containing the targetpoint(s) on the target area) to the viewer via a 3D display. The viewer,in turn, may edit the displayed path by manipulating the displayed path.The viewer may manipulate the displayed path using any suitable type ofinput including, but not limited, to the above-described types of inputfrom manually specifying paths.

The path at least partially intersecting the target area may be anysuitable type of path. As previously described, the path may indicate asequence of target points along which HIFU (e.g., at least one focusedHIFU beam) is to be applied. The target points in the sequence may beordered in any suitable way and, for example, may be ordered inaccordance with a raster scan of the target area, as a non-limitingembodiment.

After the path for the application of HIFU 15 identified, the process4500 proceeds to act 4506, where one or more HIFU control parametersused for applying HIFU along the path are calculated. The followingdescription assumes the HIFU control parameters are calculated, thoughthey may be determined in other manners in other embodiments. The HIFUcontrol parameters are calculated in such a way that when the systemexecuting process 4500 applies HIFU to the target area based on thecalculated HIFU parameters, HIFU is applied along points in theidentified path using at least one HIFU beam. In some embodiments, theHIFU control parameters are calculated based at least in part on userinput specifying how much energy and/or power to apply to each pointalong the path. For example, such input may specify different energyand/or power levels depending on whether HIFU is used to heat,cauterize, or ablate the tissue along the path of a HIFU beam.

In some embodiments, the HIFU control parameters specify how an array ofultrasound elements (e.g., array 402 a) may transmit signals to form thefocused HIFU beam. In such embodiments, the HIFU parameters may becalculated by using a beamforming technique (e.g., sphericallyconverging wave front beamforming), a focusing technique (e.g., timereversal focusing), and/or any other suitable technique. In someembodiments, the beamforming and/or focusing techniques may take intoaccount speed of wave propagation in the medium to which the HIFU isapplied and/or refraction.

After HIFU parameters are calculated in act 4506, the process 4500proceeds to act 4508, where at least one HIFU beam is applied to thetarget area based at least in part on the calculated HIFU parameters.After the HIFU is applied, process 4500 completes.

It should be appreciated that process 4500 is illustrative and thatthere are variations of process 4500. For example, in some embodiments,instead of calculating a path at least partially intersecting a targetarea, it may be determined (e.g., based on user input or automatically)that HIFU is to be applied to the entire target area or a shell aroundthe target area. In such embodiments, HIFU parameters are determinedsuch that HIFU is applied by spreading HIFU energy along the entiretarget area or the shell around the target area.

As a non-limiting example of the operation of process 4500, a user mayidentify the target area of a subject at act 4502 by viewing a 3D imageof the subject. The user may extract a 3D subvolume of the 3D image(e.g., extract a portion of an imaged kidney) and plan the HIFU paththrough the subvolume. In considering the path, the viewer maymanipulate the subvolume, for instance by rotating the image of thesubvolume, enlarging the image of the subvolume, or manipulating theimage of the subvolume in any other suitable manner The view may thenidentify the locations of interest within the subvolume that are to makeup the HIFU path. A system (e.g., a computer system) being used toperform the process 4500 may record the points making up the desiredHIFU path identified by the viewer. In some embodiments, registrationbetween a subvolume of a 3D image extracted from a larger 3D image maybe maintained by the system, such that if a surgical path (e.g., a pathalong which a focused HIFU beam may be applied) is planned with respectto the extracted subvolume, the path may be accurately translated to thelarger 3D image. Such processing (including viewing of the 3D image andany extracted subvolume) may proceed in real time in some embodiments.

The inventors have appreciated that it may be useful to adjust the wayin which HIFU is applied to a subject in response to motion of thesubject. For example, when a HIFU beam is applied to heat, cauterize,and/or ablate a target area of tissue in a subject and the subject movescausing the target area of tissue to move from one position to anotherposition, the HIFU beam may need to be adjusted so that it is stillapplied to the target area after the patient movement. This way, theHIFU beam may be applied only to a target area of tissue (e.g., diseasedtissue) to which the application of a HIFU beam is planned, hereinreferred to as a planned target area, and may not be applied,inadvertently, to other areas of tissue (e.g., healthy tissue) as aresult of the subject's motion.

The inventors have further appreciated that one or more images of asubject, obtained while HIFU energy is being applied to the subject, maybe used to adjust the way in which HIFU is being applied to the subject.Such image(s) of the subject may be used to detect whether HIFU is beingapplied to a planned target area or areas in the subject (e.g., asdetermined by a doctor and/or in any other suitable way) or is beingapplied to other areas in the subject (e.g., due to motion of thesubject). This may be done in any suitable way. For example, in someembodiments, image(s) of the subject may be used to identify an area towhich the HIFU beam has been applied. The position of the identifiedarea may be compared with the position of a planned target area, and themanner in which the HIFU beam is applied to the subject may be adjustedbased on results of the comparison. For example, the HIFU beam may beadjusted to apply energy to one or more different positions in thesubject to maintain the focus of the HIFU beam on a planned target areain the subject, even as the subject moves. These and other embodimentsare described in more detail below with reference to FIG. 46, whichshows an illustrative process 4600 for adjusting application of a HIFUbeam to a subject based on one or more images of the subject. Process4600 may be performed by any suitable controller configured to controlHIFU beams produced by one or more ultrasound arrays, an example ofwhich is control system 406 described with reference to FIG. 4. Aspreviously described, control system 406 is configured to control one ormore HIFU beams produced by opposed arrays 402 a and 402 b.

It should be appreciated that image(s) of the subject may be used toadjust the way in which HIFU is being applied to the subject in otherways. For example, image(s) of the subject may be used to determinewhether HIFU is being applied to an appropriately sized area of thesubject. For example, the image(s) may be used to determine whether theHIFU beam is applied to a larger area of the subject than planned and/ora smaller area of the subject than planned.

Process 4600 begins at act 4602, where one or more multiple targetpoints for application of HIFU in a subject are identified. The targetpoint(s) may be identified in any suitable way and, for example, may beobtained in the manner previously described with reference to act 4504in FIG. 45. In some embodiments, a volumetric image of a subject may bedisplayed (e.g., with a 3D display) and a user may identify targetpoints using the displayed volumetric image, for example using handmotions, a point device (e.g., stylus pen), or in another suitablemanner, examples of which have been described herein. In someembodiments, the target points may be identified automatically. This maybe done in any suitable way. For example, target points may beidentified automatically by using any suitable computer vision and/orimage understanding techniques including, but not limited to,segmentation, boundary estimation, ellipsoid fitting, and detection withshape descriptor metrics. In some embodiments, target points may beidentified automatically by using one or more other sensors. The targetpoint(s) may lie along a path through the subject.

After the target point(s) for application of HIFU are identified,process 4600 proceeds to act 4603, where HIFU energy is applied to oneor more of the identified target points. This may be done in anysuitable way and, for example, may be done as described with referenceto acts 4506 and 4508 of process 4500. That is, for example, one or moreHIFU control parameters may be calculated and HIFU energy may be appliedto the identified target point(s) based on the HIFU controlparameter(s).

Next, process 4600 proceeds to act 4604, where one or more images of thesubject are obtained. In some embodiments, one or more volumetric imagesof the subject may be obtained. The volumetric image(s) may be obtainedin any suitable way, examples of which were previously described withreference to process 2900 in FIG. 29. The volumetric images(s) of anysuitable type may be obtained including, but not limited to, one or morevolumetric images computed from only time-of-flight measurements, onlyattenuation measurements, or any suitable combination thereof. Someembodiments described herein are not limited to obtaining onlyvolumetric images of the subject as part of act 4604, and other types ofimages (e.g., two-dimensional images, B-scan images, etc.) of thesubject may be obtained in addition to or instead of volumetric imagesof the subject.

In some embodiments, the volumetric image(s) obtained at act 4604 may becomputed from measurements obtained, at least in part, by the same arrayor arrays that generate the HIFU beam in process 4600. For example,arrays 402 a and 402 b, described with reference to FIG. 4, may be usedto image the subject as well as to generate and apply a HIFU beam to thesubject. However, in other embodiments, different arrays may be used forimaging a subject and generating and applying a HIFU beam to thesubject.

In some embodiments, one or more image shape analysis techniques may beapplied to each image of the subject obtained in act 4604. Any suitableimage shape analysis technique may be applied, examples of which werepreviously described with reference to act 4106 of process 4100. Theimage shape analysis techniques may be applied to image(s) of thesubject before or the after the images(s) are obtained at act 4604.

After one or more images of the subject are obtained at act 4604, theprocess 4600 proceeds to act 4606, where the image(s) are used toidentify one or more positions in the subject to which HIFU energy(e.g., a HIFU beam) has been applied. Each image obtained in act 4604may be processed on its own to identify one or more positions to which aHIFU beam has been applied. This may be done in any suitable way, forexample, by detecting features in the image indicative of theapplication of the HIFU beam and tracking the path of these featuresthrough the image. When multiple images are obtained in act 4604, theimages may be jointly processed to identify the positions, in each ofthe multiple images, to which a HIFU beam has been applied.

Regardless of whether a single or multiple images are processed as partof act 4606, any suitable techniques may be used to process the image(s)to detect and/or track positions in the subject to which a HIFU beam hasbeen applied. In some embodiments, statistical inference techniques maybe used to detect and/or track the positions including, but not limitedto, least-squares fitting, Kalman filtering, extended Kalman filtering,unscented Kalman filtering, particle filtering, tracking as inference,and/or any other suitable technique.

After one or more positions to which a HIFU beam has been applied areidentified by processing the images obtained in act 4604, the process4600 proceeds to decision block 4608, where it is determined whether theposition(s) to which the HIFU beam is being applied should be corrected.This determination may be made in any suitable way, and may beautomatic. For example, in some embodiments, the positions identifiedfrom imaging data in act 4604 may be compared with positions in theplanned path of positions obtained in act 4602. The comparison may beperformed by calculating the difference between the identified andplanned positions, the ratio between the identified and plannedpositions, or in any other suitable way. When it is determined that theidentified positions do not significantly deviate from the plannedpositions (e.g., when the difference between the identified and plannedpositions is below a threshold), it may be determined that the HIFU beamneed not be adjusted. Accordingly, parameters controlling the positionsto which the HIFU beam is to be applied are left unchanged and HIFUenergy may continue to be applied to the same target point(s) to whichHIFU energy has been applied. Process 4600 returns to act 4603 and acts4603-4606 are repeated. In this way, process 4600 continues to monitorthe subject, by using images of the subject, to determine whether anyadjustments should be made to the HIFU beam.

On the other hand, when it is determined, at decision block 4608, thatthe identified positions deviate from the planned positions (e.g., whenthe difference between the identified and planned positions of the HIFUbeam is above a threshold), it may be determined that the HIFU beam isto be adjusted (e.g., by adjusting the positions to which the HIFU beamis to be applied). For example, when a subject moves while a HIFU beamis being applied to the subject, images of the subject may indicate thatthe HIFU beam has been applied to one or more positions that deviatefrom the planned positions. This may provide an indication that the HIFUbeam should be adjusted to compensate for the subject's motion.

If it is determined that the HIFU beam should be corrected (e.g.,because the location to which the HIFU beam was being applied (which maybe referred to as a target point) does not match the desired location(which may be referred to as a planned point) for application of theHIFU), process 4600 proceeds to act 4610, where a HIFU beam correctionmay be determined (e.g., calculated). This may be done in any suitableway. In some embodiments, differences between the identified and plannedpositions of the HIFU beam may be used to adjust one or more HIFUcontrol parameters that control the position(s) to which the HIFU beamis being applied or the position(s) to which the HIFU beam is to beapplied. For example, differences between the identified and plannedpositions of the HIFU beam may be used to calculate a HIFU steeringvector which, in turn, may be used to adjust the position(s) to whichthe HIFU beam is being applied. In some embodiments, the differencebetween the identified and planned positions of the HIFU beam may beprocessed (e.g., by integrating and/or smoothing changes over time) tostabilize the way in which the HIFU beam is controlled so thatadjustments to the HIFU beam are not made in response to fluctuationsdue to noise or other spurious anomalies in the imaging data.

After the HIFU beam correction has been computed, at act 4610, process4600 proceeds to act 4612, where the HIFU beam correction is used toadjust one or more parameters controlling the positions to which theHIFU beam is applied. In turn, the corrected HIFU beam may be applied tothe subject.

Next, process 4600 proceeds to decision block 4614, where it isdetermined whether the HIFU beam has been applied along the entirety ofthe planned HIFU path obtained at act 4602. This determination may bemade in any suitable way and, for example, may be made by comparing thepositions to which the HIFU beam has been applied with the positions inthe planned HIFU path. If the HIFU beam has been applied to all thepositions of the planned path, process 4600 completes. Otherwise,process 4600 returns to act 4603.

Processes 4500 and 4600 may utilize various levels of automation. Forexample, one or more acts in each process may be automated. In someembodiments, process 4500 and/or 4600 may be fully automated. AutomaticHIFU control (e.g., automatic focusing of a HIFU beam, automatictracking of a HIFU beam, automatic identification of one or more targetpoints to which HIFU energy has been applied (e.g., via a HIFU beam))may therefore be provided according to some embodiments describedherein.

The timing of the processes illustrated in FIGS. 41 and 44-46 mayconform to any desired timing schemes. In some embodiments, real timeimaging and image manipulation may be desired. Thus, according to someaspects, one or more acts shown in FIGS. 41 and 44-46 may be performedin real time. In some embodiments, in-situ real time image guidedsurgery with HIFU may be provided. Alternative timings are alsopossible.

Having thus described several aspects and embodiments of the technologydescribed in the application, it is to be appreciated that variousalterations, modifications, and improvements will readily occur to thoseskilled in the art. Such alterations, modifications, and improvementsare intended to be within the spirit and scope of the technologydescribed in the application. For example, those of ordinary skill inthe art will readily envision a variety of other means and/or structuresfor performing the function and/or obtaining the results and/or one ormore of the advantages described herein, and each of such variationsand/or modifications is deemed to be within the scope of the embodimentsdescribed herein. Those skilled in the art will recognize, or be able toascertain using no more than routine experimentation, many equivalentsto the specific embodiments described herein. It is, therefore, to beunderstood that the foregoing embodiments are presented by way ofexample only and that, within the scope of the appended claims andequivalents thereto, inventive embodiments may be practiced otherwisethan as specifically described. In addition, any combination of two ormore features, systems, articles, materials, kits, and/or methodsdescribed herein, if such features, systems, articles, materials, kits,and/or methods are not mutually inconsistent, is included within thescope of the present disclosure.

The above-described embodiments can be implemented in any of numerousways. One or more aspects and embodiments of the present applicationinvolving the performance of processes or methods may utilize programinstructions executable by a device (e.g., a computer, a processor, orother device) to perform, or control performance of, the processes ormethods. In this respect, various inventive concepts may be embodied asa computer readable storage medium (or multiple computer readablestorage media) (e.g., a computer memory, one or more floppy discs,compact discs, optical discs, magnetic tapes, flash memories, circuitconfigurations in Field Programmable Gate Arrays or other semiconductordevices, or other tangible computer storage medium) encoded with one ormore programs that, when executed on one or more computers or otherprocessors, perform methods that implement one or more of the variousembodiments described above. The computer readable medium or media canbe transportable, such that the program or programs stored thereon canbe loaded onto one or more different computers or other processors toimplement various ones of the aspects described above. In someembodiments, computer readable media may be non-transitory media.

The terms “program” or “software” are used herein in a generic sense torefer to any type of computer code or set of computer-executableinstructions that can be employed to program a computer or otherprocessor to implement various aspects as described above. Additionally,it should be appreciated that according to one aspect, one or morecomputer programs that when executed perform methods of the presentapplication need not reside on a single computer or processor, but maybe distributed in a modular fashion among a number of differentcomputers or processors to implement various aspects of the presentapplication.

Computer-executable instructions may be in many forms, such as programmodules, executed by one or more computers or other devices. Generally,program modules include routines, programs, objects, components, datastructures, etc. that perform particular tasks or implement particularabstract data types. Typically the functionality of the program modulesmay be combined or distributed as desired in various embodiments.

Also, data structures may be stored in computer-readable media in anysuitable form. For simplicity of illustration, data structures may beshown to have fields that are related through location in the datastructure. Such relationships may likewise be achieved by assigningstorage for the fields with locations in a computer-readable medium thatconvey relationship between the fields. However, any suitable mechanismmay be used to establish a relationship between information in fields ofa data structure, including through the use of pointers, tags or othermechanisms that establish relationship between data elements.

When implemented in software, the software code can be executed on anysuitable processor or collection of processors, whether provided in asingle computer or distributed among multiple computers.

Further, it should be appreciated that a computer may be embodied in anyof a number of forms, such as a rack-mounted computer, a desktopcomputer, a laptop computer, or a tablet computer, as non-limitingexamples. Additionally, a computer may be embedded in a device notgenerally regarded as a computer but with suitable processingcapabilities, including a Personal Digital Assistant (PDA), a smartphone or any other suitable portable or fixed electronic device.

Also, a computer may have one or more input and output devices. Thesedevices can be used, among other things, to present a user interface.Examples of output devices that can be used to provide a user interfaceinclude printers or display screens for visual presentation of outputand speakers or other sound generating devices for audible presentationof output. Examples of input devices that can be used for a userinterface include keyboards, and pointing devices, such as mice, touchpads, and digitizing tablets. As another example, a computer may receiveinput information through speech recognition or in other audibleformats.

Such computers may be interconnected by one or more networks in anysuitable form, including a local area network or a wide area network,such as an enterprise network, and intelligent network (IN) or theInternet. Such networks may be based on any suitable technology and mayoperate according to any suitable protocol and may include wirelessnetworks, wired networks or fiber optic networks.

Also, as described, some aspects may be embodied as one or more methods.The acts performed as part of the method may be ordered in any suitableway. Accordingly, embodiments may be constructed in which acts areperformed in an order different than illustrated, which may includeperforming some acts simultaneously, even though shown as sequentialacts in illustrative embodiments.

All definitions, as defined and used herein, should be understood tocontrol over dictionary definitions, definitions in documentsincorporated by reference, and/or ordinary meanings of the definedterms.

The indefinite articles “a” and “an,” as used herein in thespecification and in the claims, unless clearly indicated to thecontrary, should be understood to mean “at least one.”

The phrase “and/or,” as used herein in the specification and in theclaims, should be understood to mean “either or both” of the elements soconjoined, i.e., elements that are conjunctively present in some casesand disjunctively present in other cases. Multiple elements listed with“and/or” should be construed in the same fashion, i.e., “one or more” ofthe elements so conjoined. Other elements may optionally be presentother than the elements specifically identified by the “and/or” clause,whether related or unrelated to those elements specifically identified.Thus, as a non-limiting example, a reference to “A and/or B”, when usedin conjunction with open-ended language such as “comprising” can refer,in one embodiment, to A only (optionally including elements other thanB); in another embodiment, to B only (optionally including elementsother than A); in yet another embodiment, to both A and B (optionallyincluding other elements); etc.

As used herein in the specification and in the claims, the phrase “atleast one,” in reference to a list of one or more elements, should beunderstood to mean at least one element selected from any one or more ofthe elements in the list of elements, but not necessarily including atleast one of each and every element specifically listed within the listof elements and not excluding any combinations of elements in the listof elements. This definition also allows that elements may optionally bepresent other than the elements specifically identified within the listof elements to which the phrase “at least one” refers, whether relatedor unrelated to those elements specifically identified. Thus, as anon-limiting example, “at least one of A and B” (or, equivalently, “atleast one of A or B,” or, equivalently “at least one of A and/or B”) canrefer, in one embodiment, to at least one, optionally including morethan one, A, with no B present (and optionally including elements otherthan B); in another embodiment, to at least one, optionally includingmore than one, B, with no A present (and optionally including elementsother than A); in yet another embodiment, to at least one, optionallyincluding more than one, A, and at least one, optionally including morethan one, B (and optionally including other elements); etc.

Also, the phraseology and terminology used herein is for the purpose ofdescription and should not be regarded as limiting. The use of“including,” “comprising,” or “having,” “containing,” “involving,” andvariations thereof herein, is meant to encompass the items listedthereafter and equivalents thereof as well as additional items.

In the claims, as well as in the specification above, all transitionalphrases such as “comprising,” “including,” “carrying,” “having,”“containing,” “involving,” “holding,” “composed of,” and the like are tobe understood to be open-ended, i.e., to mean including but not limitedto. Only the transitional phrases “consisting of” and “consistingessentially of” shall be closed or semi-closed transitional phrases,respectively.

APPENDIX A

As previously described with reference to process 2900, a geometricmodel may be constructed by computing path length information. Pathlength information may be computed by using any suitable techniquesincluding, but not limited to, any of the techniques previouslydescribed with reference to process 2900. In this Appendix, additionaltechniques for computing path length information are described.

The techniques for computing path length information which are describedbelow are explained with reference to a matrix data structure that maybe used to encode path length information. Though, it should beappreciated that this is done only for clarity of exposition as pathlength information may be encoded and/or stored in any suitable way.

I. First Technique Geometric Considerations

Path length information may be computed, at least in part, bydetermining for a line segment from an ultrasound source to anultrasound sensor (e.g., from ultrasound source (i, j) to ultrasoundsensor (k, l)), which voxels (if any) of a volume being imaged areintersected by the line segment. For each voxel that is intersected bythe line segment, a value indicative of the length of the portion of theline segment that intersects the voxel may be computed. In someembodiments, the computed value may be encoded using a data structuresuch as, but not limited to, a matrix. For example, a value for a voxelintersecting the line segment from ultrasound source (i, j) toultrasound sensor (k, l) may be encoded in the (ijkl) row of matrix A,and may be encoded in a column corresponding to the voxel (e.g., column(xyz) corresponding to voxel located at coordinates (x,y,z) in thevolume being imaged).

Initially, note that the bounding planes of a voxel (i.e., planesdemarcating the faces of the voxel) may be represented simply when theplanes are aligned with Cartesian coordinates. As a result, the planarintersections between the line segment from an ultrasound source locatedat Cartesian coordinates r₀=(x₀, y₀, z₀)^(T) to an ultrasound sensorlocated at Cartesian coordinates r₁=(x₁, y₁, z₁)^(T) and the planedemarcating each face of the voxel may be computed as described below.Let r=(x, y, z)^(T) be the lowermost corner (lowest in Cartesiancomponents) of a voxel in a volume being imaged. Any point v_(η) alongthe above-described line segment may be represented according to:

v _(η) =r ₀+η(r ₁ −r ₀), 0≦η≦1,  (A.1)

where the interpolation parameter, η, indicates how far along the linesegment the point v_(η) lies. Since the interpolation parameter ηuniquely determines the location of point v_(η) along given linesegment, the point v_(η) and the interpolation parameter η are referredto interchangeably.

The intersection point between the line segment from r₀ to r₁ and thex-y plane at offset Z, may be computed by solving (A.1) in thez-component to find η according to:

$\begin{matrix}{\eta = {\frac{z - z_{0}}{z_{1} - z_{0}}.}} & \left( {A{.2}} \right)\end{matrix}$

The other components of the intersection point v_(η) may then becomputed using (A.1). Note that the form of equation A.2 remains thesame for planes in the other two mutually orthogonal orientations (i.e.,the x-z plane and the y-z plane). Also note that the length of thesub-segment from two points represented at least in part byinterpolation parameters η₁ and η₂ is given according to:

$\begin{matrix}\begin{matrix}{{{v_{\eta_{2}} - v_{\eta_{1}}}} = {{\left\lbrack {r_{0} + {\eta_{2}\left( {r_{1} - r_{0}} \right)}} \right\rbrack - \left\lbrack {r_{0} + {\eta_{1}\left( {r_{1} - r_{0}} \right)}} \right\rbrack}}} \\{= {\left( {\eta_{2} - \eta_{1}} \right){\left( {r_{1} - r_{0}} \right).}}}\end{matrix} & \left( {A{.3}} \right)\end{matrix}$

Thus, if the interpolation parameters of each intersection point betweena line segment and a voxel are computed, the intersection segment length(and e.g., the corresponding entry of the matrix A) may be computed.

Illustrative Process for Constructing Geometry Model

A technique for constructing a geometry model including path lengthinformation is now described below. The technique relies on theabove-described geometric principles. Consider a line segment from anultrasound source positioned at r₀=(x₀, y₀, z₀)^(t) to an ultrasoundsensor positioned at r₁=(x₁, y₁, z₁)^(t). To compute the lengths ofportions of a line segment (from the ultrasound source to the ultrasoundsensor) intersecting each voxel along the line segment (e.g., to computethe entries of the row of the matrix A that corresponds to theabove-identified source-sensor pair), the technique comprises computinginterpolation parameters, η, for the intersections of the line segmentwith all of the planes defining the voxel boundaries. For example, tocompute the interpolation parameters of the intersections of the x-yplanes with the line segment at offsets z_(i), equation A.2 may be usedto compute:

$\begin{matrix}{\eta_{z_{i}} = {\frac{z_{i} - z_{0}}{z_{1} - z_{0}}.}} & \left( {A{.4}} \right)\end{matrix}$

Similarly, equation A.2 may be used to compute the interpolationparameters of the intersections of the x-z planes with the line segmentat offsets y_(i), and the interpolation parameters of the intersectionsof the y-z planes with the line segment at offsets x_(i), for all voxelboundary planes. If the computed interpolation parameter of anintersection point is less than 0 or is greater than 1, then such anintersection point is not within the extents of the line segment (i.e.,it intersects the continuation of the line segment), and theintersection point is discarded from further consideration. It should beappreciated that the above-described computation may be vectorized, forexample, by storing the offsets {x_(i)}, {y_(i)}, and {z_(i)} in machinevectors and using vector operations to compute equation A.4 and itsanalogues. Furthermore, if the offsets {x_(i)}, {y_(i)}, and {z_(i)} aresorted prior to computing equation A.4, then the resulting vector ofinterpolation parameters will also be sorted.

The three sets of interpolation parameters {η_(x) _(i) }, {n_(y) _(i) },and {η_(z) _(i) } are then merged into an ordered set (η_(i)) and sortedfrom smallest to largest. If the three sets of parameters are alreadyordered, then the merge and sort operations may be performed in lineartime (e.g., similarly to the “merge” step of the “merge-sort” algorithm,which is known in the art). Note that if the interpolation parametersη_(i) and η_(i+1) are distinct, then there are no intersection points ηstrictly between them, so the line segment from η_(i) to η_(i+1)describes an intersecting line sub-segment within a single voxel. Thus,the desired lengths may be obtained by iterating through (η_(i)) andcomputing the desired lengths with equation A.3 according to:

l _(i)=(η_(i+1)−η_(i))|r ₀ −r ₁|.  (A.5)

-   -   When the lengths are stored in the row of the matrix A (the row        corresponding to the above-identified source-sensor pair), a        determination is made of how to assign the lengths computed        using (A.5) to the appropriate columns within that row. This may        be done iteratively by attaching information to the intersection        points η_(i) before they merged and sorted. Each voxel can be        described by a position vector s εZ³, that indexes the position        of the voxel within the three-dimensional Cartesian integer        lattice. When the process starts, the first length computed, l₀,        corresponds to the voxel s₀, describing the voxel containing r₀.        The index of the next voxel, s₁, corresponding to the next        length computed, l₁, may be inferred from the orientation of the        plane of intersection described by the intersection point η₁. If        it were an x-y plane, then the next voxel is positioned at        s₀±(0,0,1)^(t)=s₀±e₃ (with the sign being determined by the        corresponding component of the vector r₁−r₀). To facilitate this        step of the computation, the vector ±e₃ may be associated to        each of the n_(z) _(i) as they are being computed, and similarly        for η_(x) _(i) (attaching ±e₁) and η_(y) _(i) (attaching ±e₂).        Hence, instead of sets {η_(i)}, sets of tuples b_(i)=(η_(i),        δ_(i)) are stored, where δ_(i) describes the voxel index        displacement vector corresponding to the intersection plane        orientation. The b_(i) may then be merged and sorted, with η_(i)        used as the sort key. Thus, after the length l_(i) is computed,        it may be stored in the column of the matrix A corresponding to        the voxel index given according to: s_(i)=s_(i−1)+δ_(i).

The above-described technique may be summarized as follows:

1. Given position vectors r₀ and r₁ of an ultrasound source-sensor pair,compute the interpolation parameters {n_(x) _(i) }, {η_(y) _(i) }, and{n_(z) _(i) }, from the plane offsets {x_(i)}, {y_(i)}, and {z_(i)},respectively, using equation A.4. Associated with each interpolationparameter, the corresponding displacement vector δ(±e₁ for each n_(x)_(i) , ±e₂ for each η_(y) _(i) , and ±e₃ for each n_(z) _(i) , where thesign is taken from the corresponding component of (r₁−r₀)), formingtuples {b_(x) _(i) }, {b_(y) _(i) }, and {b_(z) _(i) }.2. Merge and sort {b_(x) _(i) }, {b_(y) _(i) }, and {b_(z) _(i) }, intoan ordered set (b_(i)) using η_(i) as the sort key (from smallest tolargest).3. For each i, compute l_(i) from b_(i) and b_(i+1) according to (A.5)and assign it to voxel s_(i) where s_(i)=s_(i−1)+δ_(i), and s₀ is theindex of the voxel containing r₀.

To compute path length information and, in particular, to computeentries of the matrix A, in some embodiments, the above-describedprocess may be used to calculate entries for one or more (or all) row inthe matrix A. Specifically, the above-described process may be used tocalculate entries for the (ijkl)th row of the matrix A corresponding toa pair of an ultrasound source (i, j) and sensor (k, l).

Computational Complexity

The computational complexity of the above-described technique forcomputing path length information is analyzed below. Consider anembodiment where an ultrasound imaging device has an N_(tx)× N_(ty)array of sensors and an N_(rx)×N_(ry) array of sources configured toimage an M_(x)×M_(y)×M_(z) volume of voxels. The computationalcomplexity of the first step in the above described sequence of threesteps is linear in each of the dimensions of the volume beingimaged—i.e., the computational complexity is O(M_(x)+M_(y)+M_(z)). Aspreviously described, the sets, {b_(x) _(i) }, {b_(y) _(i) }, and {b_(z)_(i) }, may be sorted, in which case the computational complexity ofstep 2 in the above-described sequence is also linear in each of thedimensions of the volume being imaged—i.e., the computational complexityis O(M_(x)+M_(y)+M_(z)). Finally, the computational complexity of step 3is also O(M_(x)+M_(y)+M_(z)), since an O(1) calculation is performed foreach b_(i).

Since the above process may be run for each of theN_(rx)N_(ry)N_(tx)N_(tz) line segments associated with the source-sensorpairs, the computational complexity of computing path length informationfor all source sensor pairs, using this approach, isO(N_(rx)N_(ry)N_(tx)N_(tz) (M_(x)+M_(y)+M_(z))). If N were to representthe largest dimension of either array (in number of elements) and M wererepresents the largest dimension of the volume (in number of voxels),then the computational complexity would be O(N⁴M).

It should be appreciated that although the above-described technique wasdescribed with reference to a rectangular array of sources, arectangular array of sensors, and a regular volume of voxels, thetechnique may be applied in a more general setting, as aspects of thepresent application are not limited in this respect. For example, thelocations of the sources and sensors may be arbitrary, for the purposesof calculating path length information, since all that is needed is aparameterization of a line segment between a source and a sensor in asource-sensor pair. Thus, the above-described technique for computingpath length information is not limited to being applied to anyparticular configuration of sources and sensors (e.g., opposingtwo-dimensional arrays of sources and sensors). Furthermore, voxels neednot be defined by regularly spaced planes. If the planes bounding thevoxels are in mutually orthogonal orientations, then the computationalcomplexity may be given in more general terms as O(N_(linesegments)N_(voxelboundaryplanes)).

It should also be appreciated that the above-described process, as wellas any of the processes for computing path length information describedherein, may be parallelized. Calculations performed for eachsource-sensor pair (i.e., line segment) may be performed in parallel. Assuch, such processing may be performed by multiple parallel and/ordistributed processors, graphical processing units, etc. As such, thecomputation of path-length information may be computed in real time.

II. Second Technique: Generalization to Arbitrary Voxelizations

In the above-described process for computing a geometric model bycomputing path length information, each of the voxels in a volume to beimaged was assumed to be characterized by the same set of boundaryplanes and that each of the boundary planes lies in one of threemutually orthogonal orientations. The technique described below appliesin a more general setting, where the voxels may be adjacent polyhedra,such that there are no gaps among them. As an illustrative, non-limitingexample, such voxels may arise if a volume being imaged is subdividedinto voxels by means of a tessellation, such as a Voronoi tessellation.

For the purposes of described the technique, assume that each voxelv_(i), in a volume being imaged may be described by a set of boundaryplanes P_(i). In addition, let the graph G=(V, E), where the vertices inthe set of vertices V, correspond the voxels and an edge e=v_(i), v_(j)εE if and only if the voxels v_(i) and v_(j) are adjacent (i.e., thereexist unique planes pεP_(i) and q εP_(j) such that p and q are co-planarand overlap on the boundaries of the vertices v_(i) and v_(j)). Thus,each bounding plane, p_(j), has a non-empty set of associated edges,E_(j) ⊂E. The dual graph G comprises a unique vertex v_(out)εVcorresponding to the “outside” of the volume, so that the boundingplanes on the exterior of the volume have corresponding edges as well.

Geometric Considerations

Note that a plane may be defined with a point p₀, in the plane, and avector n, normal to the plane, according to:

(v−p ₀)·n=0.

Substituting (A.1) into the above equation, yields:

(r ₀+η_(i)(r ₁ −r ₀)−p ₀)·n=0,

which may be solved for η_(i) to obtain:

$\begin{matrix}{{\eta_{i} = \frac{\left( {p_{0} - r_{0}} \right) \cdot n}{\left( {r_{1} - r_{0}} \right) \cdot n}},} & \left( {A{.6}} \right)\end{matrix}$

which is a generalization of (A.4).

Equation A.6 may be used to calculate the intersection points of a linesegment (from a source to a sensor) with the bounding planes of a givenvoxel, v_(j). Initially, an intersection point η_(i) may be found foreach p_(i) εP_(j) by using equation A.6.

For a point η_(i) to be an intersection point of v_(j), it must lie onthe line segment and within the voxel (i.e., in the interior or on theboundary of the voxel as voxels are considered to be closed sets). Theintersection point lies on the line segment, when the 0≦η_(i)≦1. Let thebounding planes p_(k) εP_(j) of voxel v_(j) each be defined a pointp_(k) and a normal vector n_(k), where the normal vector points to theinterior of the voxel. A determination as to whether an arbitrary point,v, is within voxel v_(j) may be made by computing:

w _(k)=(v−p _(k))·n _(k)  (A.7)

for each plane p_(k) εP_(j). Intuitively, this is the distance that vlies “above” the plane p_(k), where positive values are “above”’ in thedirection of the interior of the voxel. Hence, if w_(k) is negative forany k, then the point is not within the voxel, otherwise it is withinthe voxel (in the interior if all positive, or on the boundaryotherwise). Thus, the criteria for a point η_(i) to be a validintersection point of v_(j) are given by:

0≦η_(i)≦1 and  (A.8)

(v _(η) _(i) −p _(k))·n _(k)≧0, ∀p _(k) εP _(j).  (A.9)

Another Illustrative Process for Constructing Geometry Model

Another illustrative technique for constructing a geometry modelincluding path length information is now described below. The techniquerelies on the above-described geometric principles. Once again, considera line segment from an ultrasound source positioned at r₀=(x₀, y₀,z₀)^(t) to an ultrasound sensor positioned at r₁=(x₁, y_(i), z₁)^(t).The process may be formulated as a “walk” from r₀ to r₁ through thevoxels. To this end, the dual graph G will be used to iterate over thevoxels.

Let s₀, the initial voxel, be the voxel enclosing r₀. Next, the nearestpoint at which the line segment from r₀ to r₁ leaves the initial voxels₀ is determined. This may be done by computing the intersection pointsη_(i) between the line segment and planes in the set P₀ of boundaryplanes of voxel s₀ by using equation A.6. Those intersection pointswhich do not satisfy the criteria of (A.8) and (A.9) are eliminated. Ifthe voxel s₀ is convex, then there will be exactly one such point(unless we hit a “corner,” as described below). Otherwise, the smallestsuch η_(i) will be the unique exiting point, η⁽¹⁾.

Suppose that the exiting point, η⁽¹⁾, lies on the plane p_(j) εP₀. Ifthe exiting point is not a corner of the voxel, which may be a point atwhich multiple planes intersect, then the plane p_(j) is unique. Theedges E_(j) corresponding to p_(j) may be identified by using the dualgraph G. The next voxel, s₁, will be the voxel incident with the otherend of the edge e=(s₀, v) εE_(j) such that the intersection point η⁽¹⁾lies within voxel v. Often, there will be only one edge in E_(j), but insome instances, E_(j) may comprise multiple edges, an ambiguity whichmay occur in the limit as two bounding planes become co-planar.Repeating the process, the existing point η⁽²⁾ of s₁ may be determined,and so on. When determining the exiting point of the i'th voxel, careshould be taken to ensure that that η^((i)) be monotonic so that theentrance point (i.e., η^((i−1))) is not selected as the exiting point.The iterations proceed until the point r₁ is reached. This may bedetected in any of numerous ways including by detecting that the only ηthat satisfies (A.8) is the entrance point. At each iteration i, thelength

l _(i)=η^((i+1))−η^((i)) |r ₁ −r ₀|,  (A.10)

may be added to the matrix A to the row corresponding to thesource-sensor pair positioned at r₀=(x₀, y₀, z₀)^(t), r₁=(x₁, y₁,z₁)^(t) and the voxel s_(i), where η⁽⁰⁾=0 and η^((final+1))=1. If thevoxel s_(i) is convex, the addition will be equivalent to assignment,but non-convex voxels can be entered more than once.The above-described technique may be summarized as follows:1. Let s₀ be the voxel containing r₀ and let η⁽⁰⁾=0.2. For each i,

-   -   (a) Compute η_(j) for each p_(j)εP_(i), and let η^((i+1)) be the        smallest η_(j) that satisfies (A.8) and (A.9) and is strictly        greater than η^((i)1).    -   (b) If there is no such point, then terminate the process after        the next step is performed with η^((i+1))=1.    -   (c) Add the length l_(i), computed according to (A.10), to the        entry of A corresponding to s_(i).    -   (d) Let E_(j) ⊂E be the edges of the dual graph G corresponding        to the plane pεP_(i) containing the exiting point η^((i+1)), and        find the edge e=s_(i), vεE_(j) such that the exiting point        η^((i+1)) is within v as per (A.8) and (A.9).    -   (e) Let s_(i+1)=v and repeat.        It should be appreciated that in the corner case, the exiting        point lies on the intersection of two or more bounding planes        p_(j) εP_(i) of s_(i). In that case, associated with each p_(j)        is a voxel s_(i,j), which is the “next” voxel according to that        plane. In such a corner case, the exiting point η_(i,j) may be        computed as follows. If the candidate exiting points are        distinct, then the smallest one is the next voxel (this may        occur if the voxels are not convex). Otherwise, all the        candidate exiting points coincide with the entrance point, and        any such point may be used. However, in this case, the        constraint that no voxel is visited twice during the search for        the “next” voxel should be enforced in this case.

Computational Complexity

To analyze the computational complexity of the second technique, letN_(l) be the number of line segments (equal to N⁴ for opposedrectangular arrays of dimension N×N), |V| be the number of voxels (equalto M³ for a cubic volume of dimension M×M×M), and d be the averagedegree of the vertices in V. Also observe that the computationalcomplexity of Step 1 is O(1), so that the running time is determined byStep 2. The computational complexity of step 2a is O(d²) steps, since(on average) a point is computed for each of d planes, that each need tobe checked against the d planes. The worst case in Step 2d is O(d),corresponding to an ambiguous plane with d neighbors, which can bediscerned by an O(1) computation. Finally, in the worst-case scenario,Step 2 is repeated |V| times. Thus, the computational complexity of thesecond technique is given by O(N_(l)|V|d²). It should be appreciatedthat for most voxelizations, step 2 is actually executed O({square rootover (|V|)}) times, for a computational complexity ofO(N_(l)|V|^(1/3)d²). In the parameters of the rectangular array andcuboidal voxelization, this is O(N⁴M), where d=6 is a constant factor.Hence, asymptotically, the computational complexity of the secondtechnique is the same as that of the first. However, the first techniqueincurs a smaller storage cost (only O(M) planes must be stored insteadof O(dM³)), a smaller constant factor, and uses a simplerimplementation.

Finding s₀In the above description, it was assumed that the voxel s₀ that containsr₀ is known a priori. If this is not the case, s₀ is to be identified.One approach involves checking every voxel until one was found with anentrance point η₀ and an exit point η₁ satisfying η₀≦0≦η₁. However, thecomputational complexity of such an approach is O(|V|d²) in the worstcase. Another approach may be to use a variation of the above-describedgeneralized process. That is, to first locate a point preceding r₀(i.e., η<0) that is known to be within v_(out). For example, if we knowthat the greatest distance between any two points in the volume is W,then

$\begin{matrix}{{\eta = {- \frac{W}{{r_{1} - r_{0}}}}},} & \left( {A{.11}} \right)\end{matrix}$

will describe be such a point. Then the generalized process may beapplied with r₀

v_(η) (given by (A.11)) and r₁

r₀. When the process terminates, found S₀ (the voxel containing r₀,which is the endpoint in the re-mapped problem) will have beenidentified.

What is claimed is:
 1. An apparatus, comprising: a plurality ofradiation sources comprising a first radiation source, a secondradiation source, and a third radiation source; a first radiation sensorand a second radiation sensor; and processing circuitry coupled to thefirst radiation sensor and the second radiation sensor and configured toreceive and discriminate between, for each of the first and secondradiation sensors, respective source signals emitted by the first,second, and third radiation sources, wherein the first radiation source,the second radiation source, and the first radiation sensor lie in afirst plane, and wherein the second radiation source, the thirdradiation source, and the second radiation sensor lie in a second planedifferent than the first plane.
 2. The apparatus of claim 1, wherein thefirst radiation source is an ultrasound source.
 3. The apparatus ofclaim 2, wherein the first radiation sensor and the second radiationsensor are ultrasound radiation sensors.
 4. The apparatus of claim 1,wherein the processing circuitry is configured to receive anddiscriminate between, for each of the first and second radiationsensors, the respective source signals emitted by at least ten radiationsources of the plurality of radiation sources.
 5. The apparatus of claim4, wherein the processing circuitry is configured to receive anddiscriminate between, for each of the first and second radiationsensors, the respective source signals emitted by at least 100 radiationsources of the plurality of radiation sources.
 6. The apparatus of claim5, wherein the processing circuitry is configured to receive anddiscriminate between, for each of the first and second radiationsensors, the respective source signals emitted by at least 1,000radiation sources of the plurality of radiation sources.
 7. Theapparatus of claim 4, wherein the processing circuitry is configured toreceive and discriminate between, for each of the first and secondradiation sensors, the respective source signals emitted by between tenradiation sources and 10,000 radiation sources of the plurality ofradiation sources.
 8. The apparatus of claim 1, wherein the processingcircuitry is configured to receive and discriminate between, for each ofthe first and second radiation sensors, the respective source signalsemitted by at least 1% of the radiation sources of the plurality ofradiation sources.
 9. The apparatus of claim 8, wherein the processingcircuitry is configured to receive and discriminate between, for each ofthe first and second radiation sensors, the respective source signalsemitted by at least 10% of the radiation sources of the plurality ofradiation sources.
 10. The apparatus of claim 9, wherein the processingcircuitry is configured to receive and discriminate between, for each ofthe first and second radiation sensors, the respective source signalsemitted by at least 25% of the radiation sources of the plurality ofradiation sources.
 11. The apparatus of claim 10, wherein the processingcircuitry is configured to receive and discriminate between, for each ofthe first and second radiation sensors, the respective source signalsemitted by at least 50% of the radiation sources of the plurality ofradiation sources.
 12. The apparatus of claim 11, wherein the processingcircuitry is configured to receive and discriminate between, for each ofthe first and second radiation sensors, the respective source signalsemitted by at least 75% of the radiation sources of the plurality ofradiation sources.
 13. The apparatus of claim 12, wherein the processingcircuitry is configured to receive and discriminate between, for each ofthe first and second radiation sensors, the respective source signalsemitted by at least 90% of the radiation sources of the plurality ofradiation sources.
 14. The apparatus of claim 13, wherein the processingcircuitry is configured to receive and discriminate between, for each ofthe first and second radiation sensors, the respective source signalsemitted by all radiation sources of the apparatus.
 15. The apparatus ofclaim 14, wherein the plurality of radiation sources comprises at leastfifty radiation sources.
 16. The apparatus of claim 1, wherein theplurality of radiation sources is arranged in three dimensions.
 17. Theapparatus of claim 1, wherein the plurality of radiation sources formsan array of at least two dimensions in which the plurality of radiationsources adopts a regular spacing.
 18. The apparatus of claim 17, whereinthe plurality of radiation sources is arranged in three dimensions. 19.The apparatus of claim 1, further comprising a plurality of radiationsensors including the first and second radiation sensors, wherein theplurality of radiation sensors is arranged in at least two dimensions.20. The apparatus of claim 19, wherein the plurality of radiationsensors is arranged in three dimensions.
 21. The apparatus of claim 19,wherein the plurality of radiation sensors forms an array of at leasttwo dimensions in which the plurality of radiation sensors adopts aregular spacing.
 22. The apparatus of claim 19, wherein the plurality ofradiation sources forms an array of at least two dimensions, and whereinthe plurality of radiation sensors forms an array of at least twodimensions.
 23. The apparatus of claim 1, wherein the plurality ofradiation sources and the first and second radiation sensors areconfigured to remain static during operation.
 24. The apparatus of claim1, wherein at least some radiation sources of the plurality of radiationsources are not spaced at regular intervals with respect to neighboringradiation sources.
 25. The apparatus of claim 1, further comprising aplurality of radiation sensors including the first and second radiationsensors, wherein at least some radiation sensors of the plurality ofradiation sensors are not spaced at regular intervals with respect toneighboring radiation sensors.
 26. The apparatus of claim 1, wherein theplurality of radiation sources are physically coupled to a first mountand wherein the first and second radiation sensors are physicallycoupled to a second mount.
 27. The apparatus of claim 26, wherein thefirst mount is flexible.
 28. The apparatus of claim 26, wherein thefirst and second mounts are configured to be independently movable. 29.The apparatus of claim 28, further comprising a detector configured todetect an orientation and/or position of one or more of the plurality ofradiation sources relative to one or both of the first and secondradiation sensors.
 30. The apparatus of claim 1, wherein the first andsecond radiation sensors are disposed on a first side of a plane andwherein the plurality of radiation sources are disposed on a second sideof the plane.
 31. The apparatus of claim 1, wherein the first, second,and third radiation sources and the first and second radiation sensorsare collectively configured to operate in a transmissive modality. 32.The apparatus of claim 1, wherein directivity vectors of the first,second, and third radiation sources are incident upon the first andsecond radiation sensors.
 33. The apparatus of claim 1, wherein at leastone of the first, second, and third radiation sources is configured toalternately operate as a radiation source and a radiation sensor. 34.The apparatus of claim 33, wherein the first, second, and thirdradiation sources are coupled to the processing circuitry via paralleltransmit and receive signal paths, and wherein the apparatus furthercomprises a switch for switchably coupling the first, second, and thirdradiation sources to either the transmit signal path or the receivesignal path.
 35. The apparatus of claim 1, wherein the plurality ofradiation sources comprises at least two distinct arrays of radiationsources.
 36. The apparatus of claim 35, wherein the at least twodistinct arrays of radiation sources comprises three or more distinctarrays of radiation sources.
 37. The apparatus of claim 36, wherein theprocessing circuitry coupled to the first radiation sensor and thesecond radiation sensor is configured to receive and discriminatebetween, for each of the first and second radiation sensors, respectivesource signals emitted by at least one radiation source in each of threedistinct arrays of the three or more distinct arrays of radiationsources.
 38. The apparatus of claim 1, wherein the processing circuitryis configured to perform a heterodyning function to receive anddiscriminate between the respective source signals emitted by the first,second, and third radiation sources.
 39. The apparatus of claim 38,wherein the processing circuitry comprises a multiplier configured toreceive an output signal from the first radiation sensor and atransmission signal to be emitted from the first radiation source, andwherein the multiplier is configured to provide an output signal to ananalog-to-digital converter.
 40. The apparatus of claim 1, wherein theprocessing circuitry comprises analog pulse compression circuitryconfigured to perform analog pulse compression on the respective sourcesignals emitted by the first, second, and third radiation sources andreceived by the first and second radiation sensors.
 41. The apparatus ofclaim 1, wherein the processing circuitry comprises an amplificationstage coupled directly to a detector.
 42. The apparatus of claim 1,wherein the processing circuitry comprises an amplification stagecoupled to an input of an analog-to-digital converter (ADC).
 43. Theapparatus of claim 1, wherein the plurality of radiation sources and thefirst and second radiation sensors are configured to characterize avolume, and wherein the apparatus comprises a processor configured toconstruct a three-dimensional (3D) image of the volume based at leastpartially on the respective source signals emitted by the first, second,and third radiation sources and received by the first and secondradiation sensors.
 44. The apparatus of claim 43, wherein the processorcomprises the processing circuitry.
 45. The apparatus of claim 1,wherein the plurality of radiation sources and the first and secondradiation sensors are configured to characterize a volume, and whereinthe apparatus comprises a processor configured to construct athree-dimensional (3D) temperature profile of the volume based at leastpartially on the respective source signals emitted by the first, second,and third radiation sources.
 46. The apparatus of claim 45, wherein theprocessor comprises the processing circuitry.
 47. The apparatus of claim1, further comprising a plurality of radiation sensors in addition tothe first and second radiations sensors, wherein the plurality ofradiation sources, the first and second radiation sensors, and theplurality of radiation sensors in addition to the first and secondradiation sensors collectively form a structure into which a subject maybe inserted.
 48. The apparatus of claim 47, wherein the structure issubstantially a box with an open side via which the subject may beinserted, and wherein the first and second radiation sensors togetherwith the plurality of radiation sensors in addition to the first andsecond radiation sensors form a side of the box.
 49. The apparatus ofclaim 1, wherein the apparatus further comprises at least one radiationsensor in addition to the first and second radiation sensors, the atleast one radiation sensor in addition to the first and second radiationsensors being coupled to the processing circuitry.
 50. The apparatus ofclaim 1, further comprising a plurality of ultrasound elementsconfigured as high intensity focused ultrasound (HIFU) elementsconfigured to apply HIFU.
 51. The apparatus of claim 50, furthercomprising a support on which the plurality of radiation sources and theHIFU elements are disposed.
 52. The apparatus of claim 1, wherein thefirst radiation source and the first radiation sensor are formed ofdifferent materials.
 53. The apparatus of claim 52, wherein the firstradiation source is an ultrasound source comprising lead zirconatetitanate (PZT) and wherein the first radiation sensor is an ultrasoundsensor comprising polyvinylidene difluoride (PVDF).
 54. The apparatus ofclaim 43, wherein the at least one processor is configured to constructthe 3D image of the volume by: generating a 3D image of the volume froma plurality of measurements by using a compressive sensing imagereconstruction process, the plurality of measurements obtained based atleast partially on the respective source signals.
 55. The apparatus ofclaim 54, wherein using the compressive sensing image reconstructionprocess comprises identifying a solution to a system of linear equationsrelating the plurality of measurements to a property of the volume beingimaged.
 56. The apparatus of claim 55, wherein the system of linearequations represents a linear approximation to a forward operator of athree-dimensional wave propagation equation.
 57. An apparatus,comprising: a plurality of radiation sources comprising a firstradiation source, a second radiation source, and a third radiationsource; a first radiation sensor and a second radiation sensor; andprocessing circuitry coupled to the first radiation sensor and thesecond radiation sensor and configured to receive and discriminatebetween, for each of the first and second radiation sensors, respectivesource signals emitted by the first, the second, and the third radiationsources, wherein respective center points of the first radiation source,the second radiation source, the third radiation source, and the firstradiation sensor define a first non-zero solid angle having its vertexpositioned at the center point of the first radiation sensor, andwherein the respective center points of the first radiation source, thesecond radiation source, and the third radiation source, together with acenter point of the second radiation sensor define a second non-zerosolid angle having its vertex positioned at the center point of thesecond radiation sensor.
 58. The apparatus of claim 57, wherein thefirst radiation source is an ultrasound source.
 59. The apparatus ofclaim 58, wherein the first radiation sensor and the second radiationare ultrasound radiation sensors.
 60. The apparatus of claim 57, whereinthe processing circuitry is configured to receive and discriminatebetween, for each of the first and second radiation sensors, therespective source signals emitted by at least ten radiation sources ofthe plurality of radiation sources.
 61. The apparatus of claim 60,wherein the processing circuitry is configured to receive anddiscriminate between, for each of the first and second radiationsensors, the respective source signals emitted by at least 100 radiationsources of the plurality of radiation sources.
 62. The apparatus ofclaim 61, wherein the processing circuitry is configured to receive anddiscriminate between, for each of the first and second radiationsensors, the respective source signals emitted by at least 1,000radiation sources of the plurality of radiation sources.
 63. Theapparatus of claim 60, wherein the processing circuitry is configured toreceive and discriminate between, for each of the first and secondradiation sensors, the respective source signals emitted by between tenradiation sources and 10,000 radiation sources of the plurality ofradiation sources.
 64. The apparatus of claim 57, wherein the processingcircuitry is configured to receive and discriminate between, for each ofthe first and second radiation sensors, the respective source signalsemitted by at least 1% of the radiation sources of the plurality ofradiation sources.
 65. The apparatus of claim 64, wherein the processingcircuitry is configured to receive and discriminate between, for each ofthe first and second radiation sensors, the respective source signalsemitted by at least 10% of the radiation sources of the plurality ofradiation sources.
 66. The apparatus of claim 65, wherein the processingcircuitry is configured to receive and discriminate between, for each ofthe first and second radiation sensors, the respective source signalsemitted by at least 25% of the radiation sources of the plurality ofradiation sources.
 67. The apparatus of claim 66, wherein the processingcircuitry is configured to receive and discriminate between, for each ofthe first and second radiation sensors, the respective source signalsemitted by at least 50% of the radiation sources of the plurality ofradiation sources.
 68. The apparatus of claim 67, wherein the processingcircuitry is configured to receive and discriminate between, for each ofthe first and second radiation sensors, the respective source signalsemitted by at least 75% of the radiation sources of the plurality ofradiation sources.
 69. The apparatus of claim 68, wherein the processingcircuitry is configured to receive and discriminate between, for each ofthe first and second radiation sensors, the respective source signalsemitted by at least 90% of the radiation sources of the plurality ofradiation sources.
 70. The apparatus of claim 69, wherein the processingcircuitry is configured to receive and discriminate between, for each ofthe first and second radiation sensors, the respective source signalsemitted by all radiation sources of the apparatus.
 71. The apparatus ofclaim 70, wherein the plurality of radiation sources comprises at leastfifty radiation sources.
 72. The apparatus of claim 57, wherein theplurality of radiation sources is arranged in three dimensions.
 73. Theapparatus of claim 57, wherein the plurality of radiation sources formsan array of at least two dimensions in which the plurality of radiationsources adopts a regular spacing.
 74. The apparatus of claim 73, whereinthe plurality of radiation sources is arranged in three dimensions. 75.The apparatus of claim 57, further comprising a plurality of radiationsensors including the first and second radiation sensors, wherein theplurality of radiation sensors is arranged in at least two dimensions.76. The apparatus of claim 75, wherein the plurality of radiationsensors is arranged in three dimensions.
 77. The apparatus of claim 75,wherein the plurality of radiation sensors forms an array of at leasttwo dimensions in which the plurality of radiation sensors adopts aregular spacing.
 78. The apparatus of claim 75, wherein the plurality ofradiation sources forms an array of at least two dimensions, and whereinthe plurality of radiation sensors forms an array of at least twodimensions.
 79. The apparatus of claim 57, wherein the plurality ofradiation sources and the first and second radiation sensors areconfigured to remain static during operation.
 80. The apparatus of claim57, wherein at least some radiation sources of the plurality ofradiation sources are not spaced at regular intervals with respect toneighboring radiation sources.
 81. The apparatus of claim 57, furthercomprising a plurality of radiation sensors including the first andsecond radiation sensors, wherein at least some radiation sensors of theplurality of radiation sensors are not spaced at regular intervals withrespect to neighboring radiation sensors.
 82. The apparatus of claim 57,wherein the plurality of radiation sources are physically coupled to afirst mount and wherein the first and second radiation sensors arephysically coupled to a second mount.
 83. The apparatus of claim 82,wherein the first mount is flexible.
 84. The apparatus of claim 82,wherein the first and second mounts are configured to be independentlymovable.
 85. The apparatus of claim 84, further comprising a detectorconfigured to detect an orientation and/or position of one or more ofthe plurality of radiation sources relative to one or both of the firstand second radiation sensors.
 86. The apparatus of claim 57, wherein thefirst and second radiation sensors are disposed on a first side of aplane and wherein the plurality of radiation sources are disposed on asecond side of the plane.
 87. The apparatus of claim 57, wherein thefirst, second, and third radiation sources and the first and secondradiation sensors are collectively configured to operate in atransmissive modality.
 88. The apparatus of claim 57, whereindirectivity vectors of the first, second, and third radiation sourcesare incident upon the first and second radiation sensors.
 89. Theapparatus of claim 57, wherein at least one of the first, second, andthird radiation sources is configured to alternately operate as aradiation source and a radiation sensor.
 90. The apparatus of claim 89,wherein the first, second, and third radiation sources are coupled tothe processing circuitry via parallel transmit and receive signal paths,and wherein the apparatus further comprises a switch for switchablycoupling the first, second, and third radiation sources to either thetransmit signal path or the receive signal path.
 91. The apparatus ofclaim 57, wherein the plurality of radiation sources comprises at leasttwo distinct arrays of radiation sources.
 92. The apparatus of claim 91,wherein the at least two distinct arrays of radiation sources comprisesthree or more distinct arrays of radiation sources.
 93. The apparatus ofclaim 92, wherein the processing circuitry coupled to the firstradiation sensor and the second radiation sensor is configured toreceive and discriminate between, for each of the first and secondradiation sensors, respective source signals emitted by at least oneradiation source in each of three distinct arrays of the three or moredistinct arrays of radiation sources.
 94. The apparatus of claim 57,wherein the processing circuitry is configured to perform a heterodyningfunction to receive and discriminate between the respective sourcesignals.
 95. The apparatus of claim 94, wherein the processing circuitrycomprises a multiplier configured to receive an output signal from thefirst radiation sensor and a transmission signal to be emitted from thefirst radiation source, and wherein the multiplier is configured toprovide an output signal to an analog-to-digital converter.
 96. Theapparatus of claim 57, wherein the processing circuitry comprises analogpulse compression circuitry configured to perform analog pulsecompression on the respective source signals emitted by the first,second, and third radiation sources.
 97. The apparatus of claim 57,wherein the processing circuitry comprises an amplification stagecoupled directly to a detector.
 98. The apparatus of claim 57, whereinthe processing circuitry comprises an amplification stage coupled to aninput of an analog-to-digital converter (ADC).
 99. The apparatus ofclaim 57, wherein the plurality of radiation sources and the first andsecond radiation sensors are configured to characterize a volume, andwherein the apparatus comprises a processor configured to construct athree-dimensional (3D) image of the volume based at least partially onthe respective source signals emitted by the first, second, and thirdradiation sources and received by the first and second radiationsensors.
 100. The apparatus of claim 99, wherein the processor comprisesthe processing circuitry.
 101. The apparatus of claim 57, wherein theplurality of radiation sources and the first and second radiationsensors are configured to characterize a volume, and wherein theapparatus comprises a processor configured to construct athree-dimensional (3D) temperature profile of the volume based at leastpartially on the respective source signals emitted by the first, second,and third radiation sources and received by the first and secondradiation sensors.
 102. The apparatus of claim 101, wherein theprocessor comprises the processing circuitry.
 103. The apparatus ofclaim 57, wherein the first non-zero solid angle covers greater than π/4steradians.
 104. The apparatus of claim 103, wherein the first non-zeroangle covers greater than π/2 steradians.
 105. The apparatus of claim103, wherein the second non-zero solid angle covers greater than π/4steradians.
 106. The apparatus of claim 57, further comprising aplurality of radiation sensors in addition to the first and secondradiations sensors, wherein the plurality of radiation sources, thefirst and second radiation sensors, and the plurality of radiationsensors in addition to the first and second radiation sensorscollectively form a structure into which a subject may be inserted. 107.The apparatus of claim 106, wherein the structure is substantially a boxwith an open side via which the subject may be inserted, and wherein thefirst and second radiation sensors together with the plurality ofradiation sensors in addition to the first and second radiation sensorsform a side of the box.
 108. The apparatus of claim 57, wherein theapparatus further comprises at least one radiation sensor in addition tothe first and second radiation sensors, the at least one radiationsensor in addition to the first and second radiation sensors beingcoupled to the processing circuitry.
 109. The apparatus of claim 57,further comprising a plurality of ultrasound elements configured as highintensity focused ultrasound (HIFU) elements configured to apply HIFU.110. The apparatus of claim 109, further comprising a support on whichthe plurality of radiation sources and the HIFU elements are disposed.111. The apparatus of claim 57, wherein the first radiation source andthe first radiation sensor are formed of different materials.
 112. Theapparatus of claim 111, wherein the first radiation source is anultrasound source comprising lead zirconate titanate (PZT) and whereinthe first radiation sensor is an ultrasound sensor comprisingpolyvinylidene difluoride (PVDF).
 113. The apparatus of claim 99,wherein the at least one processor is configured to construct the 3Dimage of the volume by: generating a 3D image of the volume from aplurality of measurements by using a compressive sensing imagereconstruction process, the plurality of measurements obtained based atleast partially on the respective source signals.
 114. The apparatus ofclaim 113, wherein using the compressive sensing image reconstructionprocess comprises identifying a solution to a system of linear equationsrelating the plurality of measurements to a property of the volume beingimaged.
 115. The apparatus of claim 114, wherein the system of linearequations represents a linear approximation to a forward operator of athree-dimensional wave propagation equation.
 116. An apparatus,comprising: a plurality of radiation sources configured to emitrespective source radiation signals incident upon a volume to becharacterized, the volume spanning orthogonal X, Y, and Z axes, theplurality of radiation sources occupying multiple locations in the Xdirection and multiple locations in the Y direction; a plurality ofradiation sensors separated from the plurality of radiation sourcesalong the Z direction and configured to sense the respective sourceradiation signals emitted by the plurality of radiation sources, theplurality of radiation sensors occupying multiple locations in the Xdirection and multiple locations in the Y direction; and processingcircuitry coupled to the plurality of radiation sensors and configuredto receive and discriminate between, for each of the plurality ofradiation sensors, the respective source signals of the plurality ofradiation sources.
 117. The apparatus of claim 116, wherein theapparatus further comprises at least one additional radiation sensor inaddition to the plurality of radiation sensors.
 118. An apparatus,comprising: a plurality of radiation sources configured to emitrespective source radiation signals directed to be incident upon asubject such that the respective source radiation signals pass throughthe subject along paths bounding a volume; a radiation sensor configuredto receive the respective source radiation signals after they passthrough the subject; and processing circuitry coupled to the radiationsensor and configured to discriminate between the respective sourceradiation signals.
 119. The apparatus of claim 118, wherein theplurality of radiation sources and the radiation sensor are static. 120.An apparatus, comprising: a plurality of radiation sources configured toemit respective source radiation signals directed to be incident acrossa surface area of a subject; first and second radiation sensors eachconfigured to sense the respective source radiation signals; andprocessing circuitry coupled to the first and second radiation sensorsand configured to receive and discriminate between, for each of thefirst and second radiation sensors, the respective source radiationsignals emitted by the plurality of radiation sources.
 121. Theapparatus of claim 120, wherein a first radiation source of theplurality of radiation sources is an ultrasound source.
 122. Theapparatus of claim 121, wherein the first radiation sensor and thesecond radiation are ultrasound radiation sensors.
 123. The apparatus ofclaim 120, wherein the plurality of radiation sources comprises at leastten radiation sources.
 124. The apparatus of claim 123, wherein theplurality of radiation sources comprises at least 100 radiation sources.125. The apparatus of claim 124, wherein the plurality of radiationsources comprises at least 1,000 radiation sources.
 126. The apparatusof claim 123, wherein the plurality of radiation sources comprisesbetween ten radiation sources and 10,000 radiation sources.
 127. Theapparatus of claim 120, wherein the plurality of radiation sources isarranged in three dimensions.
 128. The apparatus of claim 120, whereinthe plurality of radiation sources forms an array of at least twodimensions in which the plurality of radiation sources adopts a regularspacing.
 129. The apparatus of claim 128, wherein the plurality ofradiation sources is arranged in three dimensions.
 130. The apparatus ofclaim 120, further comprising a plurality of radiation sensors includingthe first and second radiation sensors, wherein the plurality ofradiation sensors is arranged in at least two dimensions.
 131. Theapparatus of claim 130, wherein the plurality of radiation sensors isarranged in three dimensions.
 132. The apparatus of claim 130, whereinthe plurality of radiation sensors forms an array of at least twodimensions in which the plurality of radiation sensors adopts a regularspacing.
 133. The apparatus of claim 130, wherein the plurality ofradiation sources forms an array of at least two dimensions, and whereinthe plurality of radiation sensors forms an array of at least twodimensions.
 134. The apparatus of claim 120, wherein the plurality ofradiation sources and the first and second radiation sensors areconfigured to remain static during operation.
 135. The apparatus ofclaim 120, wherein at least some radiation sources of the plurality ofradiation sources are not spaced at regular intervals with respect toneighboring radiation sources.
 136. The apparatus of claim 120, furthercomprising a plurality of radiation sensors including the first andsecond radiation sensors, wherein at least some radiation sensors of theplurality of radiation sensors are not spaced at regular intervals withrespect to neighboring radiation sensors.
 137. The apparatus of claim120, wherein the plurality of radiation sources are physically coupledto a first mount and wherein the first and second radiation sensors arephysically coupled to a second mount.
 138. The apparatus of claim 137,wherein the first mount is flexible.
 139. The apparatus of claim 137,wherein the first and second mounts are configured to be independentlymovable.
 140. The apparatus of claim 139, further comprising a detectorconfigured to detect an orientation and/or position of the plurality ofradiation sources relative to the first and second radiation sensors.141. The apparatus of claim 120, wherein the first and second radiationsensors are disposed on a first side of a plane and wherein theplurality of radiation sources are disposed on a second side of theplane.
 142. The apparatus of claim 120, wherein the plurality ofradiation sources and the first and second radiation sensors arecollectively configured to operate in a transmissive modality.
 143. Theapparatus of claim 120, wherein directivity vectors of first, second,and third radiation sources of the plurality of radiation sources areincident upon the first and second radiation sensors.
 144. The apparatusof claim 120, wherein at least one radiation source of the plurality ofradiation sources is configurable to alternately operate as a radiationsource and a radiation sensor.
 145. The apparatus of claim 144, whereinthe at least one radiation source is coupled to the processing circuitryvia parallel transmit and receive signal paths, and wherein theapparatus further comprises a switch for switchably coupling the atleast one radiation source to either the transmit signal path or thereceive signal path.
 146. The apparatus of claim 120, wherein theplurality of radiation sources comprises at least two distinct arrays ofradiation sources.
 147. The apparatus of claim 146, wherein the at leasttwo distinct arrays of radiation sources comprises three or moredistinct arrays of radiation sources.
 148. The apparatus of claim 147,wherein the processing circuitry coupled to the first radiation sensorand the second radiation sensor is configured to receive anddiscriminate between, for each of the first and second radiationsensors, respective source signals emitted by at least one radiationsource in each of three distinct arrays of the three or more distinctarrays of radiation sources.
 149. The apparatus of claim 120, whereinthe processing circuitry is configured to perform a heterodyningfunction to detect and discriminate the respective source signals. 150.The apparatus of claim 149, wherein the processing circuitry comprises amultiplier configured to receive an output signal from the firstradiation sensor and a transmission signal to be emitted from a firstradiation source of the plurality of radiation sources, and wherein themultiplier is configured to provide an output signal to ananalog-to-digital converter.
 151. The apparatus of claim 120, whereinthe processing circuitry comprises analog pulse compression circuitryconfigured to perform analog pulse compression on the respective sourcesignals.
 152. The apparatus of claim 120, wherein the processingcircuitry comprises an amplification stage coupled directly to adetector.
 153. The apparatus of claim 120, wherein the processingcircuitry comprises an amplification stage coupled to an input of ananalog-to-digital converter (ADC).
 154. The apparatus of claim 120,wherein the plurality of radiation sources and the first and secondradiation sensors are configured to characterize at least part of thesubject, and wherein the apparatus comprises a processor configured toconstruct a three-dimensional (3D) image of the part of the subjectbased at least partially on the respective source signals.
 155. Theapparatus of claim 154, wherein the processor comprises the processingcircuitry.
 156. The apparatus of claim 120, wherein the plurality ofradiation sources and the first and second radiation sensors areconfigured to characterize at least part of the subject, and wherein theapparatus comprises a processor configured to construct athree-dimensional (3D) temperature profile of the part of the subjectbased at least partially on the respective source signals.
 157. Theapparatus of claim 156, wherein the processor comprises the processingcircuitry.
 158. The apparatus of claim 120, wherein the surface area isbetween approximately 1 cm² and approximately 100 cm².
 159. Theapparatus of claim 158, wherein the surface area is betweenapproximately 50 cm² and approximately 100 cm².
 160. An apparatus,comprising: three radiation sources arranged in a multi-dimensional,non-linear arrangement and configured to produce respective sourcesignals; a plurality of radiation sensors; and processing circuitrycoupled to the plurality of radiation sensors and configured to receiveand discriminate between, for at least one radiation sensor of theplurality of radiation sensors, the respective source signals producedby the three radiation sources.
 161. The apparatus of claim 160, whereina first radiation source of the three radiation sources is an ultrasoundsource.
 162. The apparatus of claim 161, wherein the at least oneradiation sensor is an ultrasound radiation sensor.
 163. The apparatusof claim 160, further comprising a plurality of radiation sourcesincluding the three radiation sources, and wherein the processingcircuitry is configured to receive and discriminate between, for the atleast one radiation sensor, the respective source signals emitted by atleast ten radiation sources of the plurality of radiation sources. 164.The apparatus of claim 163, wherein the processing circuitry isconfigured to receive and discriminate between, for the at least oneradiations sensor, the respective source signals emitted by at least 100radiation sources of the plurality of radiation sources.
 165. Theapparatus of claim 164, wherein the processing circuitry is configuredto receive and discriminate between, for the at least one radiationsensor, the respective source signals emitted by at least 1,000radiation sources of the plurality of radiation sources.
 166. Theapparatus of claim 163, wherein the processing circuitry is configuredto receive and discriminate between, for the at least one radiationsensor, the respective source signals emitted by between ten radiationsources and 10,000 radiation sources of the plurality of radiationsources.
 167. The apparatus of claim 160, further comprising a pluralityof radiation sources including the three radiation sources, and whereinthe processing circuitry is configured to receive and discriminatebetween, for the at least one radiation sensor, the respective sourcesignals emitted by at least 1% of the radiation sources of the pluralityof radiation sources.
 168. The apparatus of claim 167, wherein theprocessing circuitry is configured to receive and discriminate between,for the at least one radiation sensor, the respective source signalsemitted by at least 10% of the radiation sources of the plurality ofradiation sources.
 169. The apparatus of claim 168, wherein theprocessing circuitry is configured to receive and discriminate between,for the at least one radiation sensor, the respective source signalsemitted by at least 25% of the radiation sources of the plurality ofradiation sources.
 170. The apparatus of claim 169, wherein theprocessing circuitry is configured to receive and discriminate between,for the at least one radiation sensor, the respective source signalsemitted by at least 50% of the radiation sources of the plurality ofradiation sources.
 171. The apparatus of claim 170, wherein theprocessing circuitry is configured to receive and discriminate between,for the at least one radiation sensor, the respective source signalsemitted by at least 75% of the radiation sources of the plurality ofradiation sources.
 172. The apparatus of claim 171, wherein theprocessing circuitry is configured to receive and discriminate between,for the at least one radiation sensor, the respective source signalsemitted by at least 90% of the radiation sources of the plurality ofradiation sources.
 173. The apparatus of claim 172, wherein theprocessing circuitry is configured to receive and discriminate between,for the at least one radiation sensor, the respective source signalsemitted by all radiation sources of the apparatus.
 174. The apparatus ofclaim 173, wherein the plurality of radiation sources comprises at leastfifty radiation sources.
 175. The apparatus of claim 160, furthercomprising a fourth radiation source, wherein the four radiation sourcesare arranged in three dimensions.
 176. The apparatus of claim 160,comprising a plurality of radiation sources including the threeradiation sources, wherein the plurality of radiation sources forms anarray of at least two dimensions in which the plurality of radiationsources adopts a regular spacing.
 177. The apparatus of claim 176,wherein the plurality of radiation sources is arranged in threedimensions.
 178. The apparatus of claim 160, wherein the plurality ofradiation sensors is arranged in at least two dimensions.
 179. Theapparatus of claim 178, wherein the plurality of radiation sensors isarranged in three dimensions.
 180. The apparatus of claim 178, whereinthe plurality of radiation sensors forms an array of at least twodimensions in which the plurality of radiation sensors adopts a regularspacing.
 181. The apparatus of claim 178, comprising a plurality ofradiation sources including the three radiation sources, wherein theplurality of radiation sources forms an array of at least twodimensions, and wherein the plurality of radiation sensors forms anarray of at least two dimensions.
 182. The apparatus of claim 160,wherein the three radiation sources and the plurality of radiationsensors are configured to remain static during operation.
 183. Theapparatus of claim 160, comprising a plurality of radiation sourcesincluding the three radiation sources, wherein at least some radiationsources of the plurality of radiation sources are not spaced at regularintervals with respect to neighboring radiation sources.
 184. Theapparatus of claim 160, wherein at least some radiation sensors of theplurality of radiation sensors are not spaced at regular intervals withrespect to neighboring radiation sensors.
 185. The apparatus of claim160, wherein the three radiation sources are physically coupled to afirst mount and wherein the plurality of radiation sensors arephysically coupled to a second mount.
 186. The apparatus of claim 185,wherein the first mount is flexible.
 187. The apparatus of claim 185,wherein the first and second mounts are configured to be independentlymovable.
 188. The apparatus of claim 187, further comprising a detectorconfigured to detect an orientation and/or position of the threeradiation sources relative to the plurality of radiation sensors. 189.The apparatus of claim 160, wherein the plurality of radiation sensorsare disposed on a first side of a plane and wherein the three radiationsources are disposed on a second side of the plane.
 190. The apparatusof claim 160, wherein the three radiation sources and the plurality ofradiation sensors are collectively configured to operate in atransmissive modality.
 191. The apparatus of claim 160, whereindirectivity vectors of the three radiation sources are incident uponfirst and second radiation sensors of the plurality of radiationsensors.
 192. The apparatus of claim 160, wherein at least one radiationsource of the three radiation sources is configurable to alternatelyoperate as a radiation source and a radiation sensor.
 193. The apparatusof claim 192, wherein the at least one radiation source is coupled tothe processing circuitry via parallel transmit and receive signal paths,and wherein the apparatus further comprises a switch for switchablycoupling the at least one radiation source to either the transmit signalpath or the receive signal path.
 194. The apparatus of claim 160,wherein the apparatus comprises at least two distinct arrays ofradiation sources, and wherein each of the three radiation sourcesbelongs to at least one of the at least two distinct arrays.
 195. Theapparatus of claim 194, wherein the at least two distinct arrays ofradiation sources comprises three or more distinct arrays of radiationsources.
 196. The apparatus of claim 195, wherein the processingcircuitry coupled to the plurality of radiation sensors is configured toreceive and discriminate between, for the at least one radiation sensor,respective source signals emitted by at least one radiation source ineach of three distinct arrays of the three or more distinct arrays ofradiation sources.
 197. The apparatus of claim 160, wherein theprocessing circuitry is configured to perform a heterodyning function todetect and discriminate the respective source signals.
 198. Theapparatus of claim 196, wherein the processing circuitry comprises amultiplier configured to receive an output signal from a first radiationsensor of the plurality of radiation sensors and a transmission signalto be emitted from a first radiation source of the three radiationsources, and wherein the multiplier is configured to provide an outputsignal to an analog-to-digital converter.
 199. The apparatus of claim160, wherein the processing circuitry comprises analog pulse compressioncircuitry configured to perform analog pulse compression on therespective source signals.
 200. The apparatus of claim 160, wherein theprocessing circuitry comprises an amplification stage coupled directlyto a detector.
 201. The apparatus of claim 160, wherein the processingcircuitry comprises an amplification stage coupled to an input of ananalog-to-digital converter (ADC).
 202. The apparatus of claim 160,wherein the three radiation sources and the plurality of radiationsensors are configured to characterize at least part of a subject, andwherein the apparatus comprises a processor configured to construct athree-dimensional (3D) image of the part of the subject based at leastpartially on the respective source signals.
 203. The apparatus of claim202, wherein the processor comprises the processing circuitry.
 204. Theapparatus of claim 160, wherein the three radiation sources and theplurality of radiation sensors are configured to characterize at leastpart of a subject, and wherein the apparatus comprises a processorconfigured to construct a three-dimensional (3D) temperature profile ofthe part of the subject based at least partially on the respectivesource signals.
 205. The apparatus of claim 204, wherein the processorcomprises the processing circuitry.
 206. An apparatus, comprising: aplurality of radiation sources arranged nonlinearly in a first plane orthree-dimensional space and configured to emit respective source signalsthrough a volume to be characterized; a plurality of radiation sensorsarranged nonlinearly in a second plane or three-dimensional space andconfigured to oppose the first plane or three-dimensional space, and thevolume, wherein each of the plurality of radiation sensors is configuredto sense the source signals emitted by each of the plurality ofradiation sources after the source signals pass through the volume; andprocessing circuitry coupled to the plurality of radiation sensors andconfigured to receive and discriminate between the source signals sensedby the plurality of radiation sensors, the received signals beingindicative of at least one characteristic of the volume.
 207. Theapparatus of claim 206, wherein the plurality of radiation sources isarranged nonlinearly in a plane.
 208. The apparatus of claim 207,wherein the plane is the first plane, and wherein the plurality ofradiation sensors is arranged nonlinearly in the second plane.
 209. Theapparatus of claim 207, wherein the plurality of radiation sensors isarranged nonlinearly in a three-dimensional space.
 210. The apparatus ofclaim 206, wherein the plurality of radiation sources is arrangednonlinearly in a three-dimensional space.
 211. The apparatus of claim210, wherein the plurality of radiation sensors is arranged nonlinearlyin a plane.
 212. The apparatus of claim 210, wherein thethree-dimensional space is a first three-dimensional space, and whereinthe plurality of radiation sensors is arranged nonlinearly in a secondthree-dimensional space.
 213. The apparatus of claim 206, wherein: thereceived signals are indicative of the appearance of the volume; and theapparatus further comprises image processing circuitry configured togenerate a three-dimensional image of the volume based on the receivedsignals.
 214. The apparatus of claim 206, wherein the at least onecharacteristic of the volume is a density of the volume.
 215. Theapparatus of claim 206, wherein the at least one characteristic of thevolume is a refractive index of the volume.
 216. The apparatus of claim206, wherein the plurality of radiation sources includes between ten and10,000 radiation sources.
 217. The apparatus of claim 206, wherein theplurality of radiation sensors includes between ten and 10,000 radiationsensors.
 218. The apparatus of claim 206, wherein the apparatuscomprises a processor configured to construct a three-dimensional (3D)image of the volume based at least partially on the received signals.219. The apparatus of claim 218, wherein the processor comprises theprocessing circuitry.
 220. The apparatus of claim 206, wherein theapparatus comprises a processor configured to construct athree-dimensional (3D) temperature profile of the volume based at leastpartially on the received signals.
 221. The apparatus of claim 220,wherein the processor comprises the processing circuitry.
 222. Anapparatus comprising: multiple arrays of ultrasound sources configuredto emit respective source signals; an array of ultrasound sensorsconfigured to sense the respective source signals; and processingcircuitry coupled to the array of ultrasound sensors and configured toreceive and discriminate between, for at least one ultrasound sensor ofthe array of ultrasound sensors, the respective source signals of atleast one ultrasound source from each of at least two arrays of themultiple arrays of ultrasound sources.
 223. The apparatus of claim 222,wherein the multiple arrays of ultrasound sources consist of two arraysof ultrasound sources.
 224. The apparatus of claim 222, wherein themultiple arrays of ultrasound sources comprise three arrays ofultrasound sources.
 225. The apparatus of claim 224, wherein the threearrays of ultrasound sources and the array of ultrasound sensors areconfigured, in combination, to substantially surround a subject. 226.The apparatus of claim 222, wherein the multiple arrays of ultrasoundsources comprise four arrays of ultrasound sources.
 227. The apparatusof claim 226, wherein the four arrays of ultrasound sources and thearray of ultrasound sensors are configured, in combination, tosubstantially form an imaging structure configured to receive a subject.228. An apparatus, comprising: a plurality of ultrasound sensors forminga two-dimensional or three-dimensional ultrasound sensor arrangement;and processing circuitry coupled to the plurality of ultrasound sensorsand configured to process signals from the plurality of ultrasoundsensors to produce ultrasound imaging data indicative of a subjectimaged at least in part by the plurality of ultrasound sensors, whereinat least some ultrasound sensors of the plurality of ultrasound sensorsare not spaced at regular intervals with respect to neighboringultrasound sensors.
 229. The apparatus of claim 228, wherein the atleast some ultrasound sensors of the plurality of ultrasound sensors arenot uniformly spaced along a line with respect to neighboring ultrasoundsensors.
 230. The apparatus of claim 228, wherein the at least someultrasound sensors of the plurality of ultrasound sensors are notuniformly spaced relative to a grid.
 231. The apparatus of claim 228,further comprising a support, wherein the plurality of ultrasoundsensors are physically coupled to the support and configured in a fixedrelationship with respect to each other.
 232. The apparatus of claim228, wherein spacing between neighboring ultrasound sensors of theplurality of ultrasound sensors is closer at an edge of the ultrasoundsensor arrangement than at a center of the ultrasound sensorarrangement.
 233. The apparatus of claim 228, wherein spacing betweenneighboring ultrasound sensors of the plurality of ultrasound sensors iscloser at a center of the ultrasound sensor arrangement than at an edgeof the ultrasound sensor arrangement.
 234. The apparatus of claim 228,wherein the plurality of ultrasound sensors assume a substantiallyrandom layout.
 235. The apparatus of claim 228, wherein the ultrasoundsensor arrangement is substantially an array in which a substantialpercentage of ultrasound sensors of the plurality of ultrasound sensorsare spaced at regular intervals with respect to neighboring ultrasoundsensors, and wherein placement of the at least some ultrasound sensorsrepresents deviation from the array.
 236. The apparatus of claim 235,wherein the ultrasound sensor arrangement is substantially planar,wherein the array substantially conforms to a grid, and wherein theplacement of the at least some ultrasound sensors represents deviationfrom the grid.
 237. The apparatus of claim 228, wherein a majority ofthe ultrasound sensors of the ultrasound sensor arrangement are notspaced at regular intervals with respect to neighboring ultrasoundsensors.
 238. The apparatus of claim 228, wherein a substantialpercentage of ultrasound sensors of the ultrasound sensor arrangementare not spaced at regular intervals with respect to neighboringultrasound sensors.
 239. The apparatus of claim 228, further comprisinga plurality of ultrasound sources forming a two-dimensional orthree-dimensional ultrasound source arrangement, wherein spacing betweenat least some ultrasound sources of the ultrasound source arrangementdiffers from spacing between at least some ultrasound sensors of theultrasound sensor arrangement.
 240. The apparatus of claim 228, whereinthe ultrasound sensor arrangement is formed on a first support andwherein the ultrasound source arrangement is formed on a second supportdistinct from the first support.
 241. An apparatus, comprising: aplurality of radiation sensors forming a two-dimensional orthree-dimensional sensor arrangement and configured to receive radiationof wavelength λ, emitted by one or more radiation sources, wherein aspacing between a first radiation sensor of the plurality of radiationsensors and its nearest neighboring radiation sensor of the plurality ofradiation sensors is greater than λ/2.
 242. The apparatus of claim 241,wherein at least one radiation sensor of the plurality of radiationsensors is an ultrasound sensor.
 243. The apparatus of claim 242,wherein the plurality of radiation sensors are ultrasound sensors. 244.The apparatus of claim 241, wherein the plurality of radiation sensorsare arranged in a two-dimensional or three-dimensional array in whichthe plurality of radiation sensors are regularly spaced.
 245. Theapparatus of claim 244, wherein the plurality of radiation sensors arearranged in a three-dimensional array.
 246. The apparatus of claim 244,wherein a minimum spacing between any radiation sensor of the pluralityof radiation sensors and its nearest neighbor is greater than λ/2. 247.The apparatus of claim 244, wherein the array is characterized by apitch between radiation sensors, and wherein the pitch is greater thanλ/2.
 248. The apparatus of claim 244, wherein the array is characterizedby a non-uniform pitch between radiation sensors, and wherein a minimumpitch of the array is greater than λ/2.
 249. The apparatus of claim 241,wherein the wavelength λ, corresponds to a center frequency of theradiation.
 250. The apparatus of claim 241, further comprising aplurality of radiation sources including the one or more radiationsources, wherein the plurality of radiation sources form atwo-dimensional or three-dimensional arrangement of radiation sourcesand are configured to emit the radiation.
 251. The apparatus of claim250, wherein a spacing between a first radiation source of the pluralityof radiation sources and its nearest neighboring radiation source of theplurality of radiation sources is greater than λ/2.
 252. The apparatusof claim 250, wherein a minimum spacing between any radiation source ofthe plurality of radiation sources and its nearest neighbor is greaterthan λ/2.
 253. The apparatus of claim 250, wherein the plurality ofradiation sensors are coupled to a first support and wherein theplurality of radiation sources are coupled to a second support distinctfrom the first support.
 254. The apparatus of claim 253, wherein thefirst and second supports are independently movable relative to eachother.
 255. The apparatus of claim 250, wherein the plurality ofradiation sources are arranged in a substantially planar configurationin a first plane and wherein the plurality of radiation sensors arearranged in a substantially planar configuration in a second plane. 256.The apparatus of claim 250, wherein the plurality of radiation sourcesand the plurality of radiation sensors are configured in combination tocharacterize a volume at least in part based on the radiation emitted bythe one or more radiation sources.
 257. The apparatus of claim 256,further comprising processing circuitry coupled to the plurality ofradiation sensors, wherein the processing circuitry is configured toconstruct a three-dimensional (3D) image of the volume based at leastpartially on the radiation emitted by the one or more radiation sources.258. The apparatus of claim 256, further comprising processing circuitrycoupled to the plurality of radiation sensors, wherein the processingcircuitry is configured to construct a three-dimensional (3D)temperature profile of the volume based at least partially on theradiation emitted by the one or more radiation sources.
 259. Theapparatus of claim 241, wherein the plurality of radiation sensors andthe one or more radiation sources are collectively configured to operatein a transmissive modality.
 260. The apparatus of claim 259, wherein theplurality of radiation sensors are ultrasound sensors and wherein theone or more radiation sources are ultrasound sources, and wherein theplurality of radiations sensors and the one or more radiation sourcesare collectively configured to operate in a transmissive ultrasoundmodality.
 261. The apparatus of claim 241, further comprising processingcircuitry coupled to the plurality of radiation sensors and configuredto receive and discriminate between, for at least one radiation sensorof the plurality of radiation sensors, the radiation of wavelength λ,emitted by the one or more radiation sources.
 262. The apparatus ofclaim 241, wherein λ represents a wavelength of a fundamental modefrequency of radiation emitted by the one or more radiation sources, andwherein the spacing between the first radiation sensor of the pluralityof radiation sensors and its nearest neighboring radiation sensor of theplurality of radiation sensors is greater than 2λ.
 263. The apparatus ofclaim 262, wherein the spacing between the first radiation sensor of theplurality of radiation sensors and its nearest neighboring radiationsensor of the plurality of radiation sensors is greater than 3λ.
 264. Anapparatus, comprising: a plurality of N×M radiation sources forming atwo-dimensional or three-dimensional radiation source arrangement andconfigured to produce a first plurality of N×M respective sourcesignals, wherein N is greater than or equal to M; a plurality of X×Yradiation sensors forming a two-dimensional or three-dimensionalradiation sensor arrangement; and processing circuitry coupled to theplurality of radiation sensors and configured to discriminate betweengreater than (X×Y×N) received signals from the N×M respective sourcesignals.
 265. The apparatus of claim 264, wherein at least one of theplurality of radiation sensors is an ultrasound sensor and wherein atleast one of the (X×Y×N) received signals is an ultrasound signal. 266.The apparatus of claim 264, wherein the plurality of radiation sourcesis a plurality of ultrasound sources and wherein the plurality ofradiation sensors is a plurality of ultrasound sensors.
 267. Theapparatus of claim 264, wherein the processing circuitry is configuredto discriminate between up to (X×Y×N×M) received signals from the N×Mrespective source signals.
 268. The apparatus of claim 267, wherein theprocessing circuitry is configured to discriminate between approximately(X×Y×N×M) received signals from the N×M respective source signals. 269.The apparatus of claim 267, wherein N=M=X=Y.
 270. The apparatus of claim264, wherein N=M=X=Y.
 271. The apparatus of claim 264, wherein theplurality of N×M radiation sources are configured to producesubstantially concurrently the first plurality of N×M respective sourcesignals.
 272. The apparatus of claim 264, comprising a processorconfigured to construct a three-dimensional (3D) image of a volume basedat least partially on the received signals.
 273. The apparatus of claim272, wherein the processor comprises the processing circuitry.
 274. Theapparatus of claim 264, comprising a processor configured to construct athree-dimensional (3D) temperature profile of a volume based at leastpartially on the received signals.
 275. The apparatus of claim 274,wherein the processor comprises the processing circuitry.
 276. Anapparatus, comprising: a plurality of ultrasound elements in a fixedrelationship with respect to each other and configured as ultrasoundimaging elements; and a detector configured to dynamically detect anorientation and/or position of the plurality of ultrasound elements.277. The apparatus of claim 276, wherein the detector is locatedseparately from the plurality of ultrasound elements.
 278. The apparatusof claim 276, wherein the orientation and/or position of the pluralityof ultrasound elements is a relative orientation and/or relativeposition relative to a second plurality of ultrasound elements.
 279. Theapparatus of claim 278, further comprising the second plurality ofultrasound elements, the second plurality of ultrasound elements beingconfigured as ultrasound imaging elements.
 280. The apparatus of claim279, wherein the detector is located separately from the plurality andthe second plurality of ultrasound elements.
 281. The apparatus of claim278, wherein the detector is configured to dynamically detect therelative orientation of the plurality of ultrasound elements relative tothe second plurality of ultrasound elements.
 282. The apparatus of claim278, wherein the detector is configured to dynamically detect therelative position of the plurality of ultrasound elements relative tothe second plurality of ultrasound elements.
 283. The apparatus of claim276, wherein the detector is integrated with the plurality of ultrasoundelements.
 284. The apparatus or claim 276, wherein the first pluralityof ultrasound elements is physically coupled to a first supportconfigured to maintain the plurality of ultrasound elements in the fixedrelationship with respect to each other.
 285. The apparatus of claim284, wherein the detector is physically coupled to the first support.286. The apparatus of claim 276, wherein the ultrasound elements aredisposed on a flexible support.
 287. The apparatus of claim 276, whereinthe detector comprises an accelerometer.
 288. The apparatus of claim276, wherein the detector comprises a gyroscope.
 289. The apparatus ofclaim 276, wherein the detector comprises an inertial navigation device.290. The apparatus of claim 276, wherein the detector comprises a rangefinder.
 291. The apparatus of claim 276, wherein the detector comprisesan inclinometer.
 292. The apparatus of claim 276, wherein the ultrasoundelements are arranged in two dimensions.
 293. The apparatus of claim276, wherein the ultrasound elements are arranged in three dimensions.294. The apparatus of claim 276, wherein the ultrasound elements arearranged in a substantially planar arrangement.
 295. The apparatus ofclaim 276, wherein the ultrasound elements are arranged in an array inwhich the ultrasound elements are regularly spaced from each other. 296.A method, comprising: accessing a plurality of measurements of asubject, the plurality of measurements resulting at least in part fromthe detection of ultrasound radiation by an ultrasound imaging deviceoperating in a transmissive modality; and generating, using at least oneprocessor, at least one volumetric image of the subject from theplurality of measurements by using a compressive sensing imagereconstruction process.
 297. The method of claim 296, wherein saidgenerating comprises identifying a solution to a system of linearequations relating the plurality of measurements to a property of thesubject.
 298. The method of claim 297, wherein identifying the solutionto the system of linear equations comprises using a sparsity constraintto identify the solution.
 299. The method of claim 297, whereinidentifying the solution to the system of linear equations comprisesusing a three-dimensional basis.
 300. The method of claim 299, whereinthe three-dimensional basis is a three-dimensional discrete cosinebasis, a three-dimensional discrete sine basis, or a three-dimensionalwavelet basis.
 301. The method of claim 297, wherein the ultrasoundimaging device comprises at least one source and at least one sensor,wherein the method further comprises: obtaining the system of linearequations based at least in part on geometry information indicatinglocation of the at least one source and the at least one sensor. 302.The method of claim 297, wherein the ultrasound imaging device comprisesa plurality of sources and a plurality of sensors, and wherein saidgenerating comprises using geometry information indicating location ofat least a first source in the plurality of sources and at least a firstsensor in the plurality of sensors.
 303. The method of claim 302,wherein the at least one volumetric image comprises a plurality ofvoxels, and wherein said generating comprises using the geometryinformation to calculate a value indicative of a length of a portion ofa line through a voxel in the plurality of voxels, wherein the lineintersects the voxel, and wherein the line connects the first source andthe first sensor.
 304. The method of claim 296, wherein the plurality ofmeasurements comprises a plurality of time-of-flight measurements and/ora plurality of attenuation measurements.
 305. The method of claim 296,wherein the plurality of measurements comprises the plurality oftime-of-flight measurements and the plurality of attenuationmeasurements, and wherein said generating comprises using Kramers-Kronigrelations to calculate the at least one volumetric image.
 306. Themethod of claim 296, wherein the plurality of measurements resulted atleast in part from the detection, by the ultrasound imaging device, ofultrasound radiation forward scattered from the subject.
 307. A method,comprising: accessing at least one volumetric image of a subjectcalculated using a plurality of measurements of the subject, theplurality of measurements resulting at least in part from the detectionof ultrasound radiation by an ultrasound imaging device operating in atransmissive modality; applying stereoscopic conversion to the at leastone volumetric image to obtain a first stereoscopic image and a secondstereoscopic image; and displaying three-dimensionally, via athree-dimensional display, the first stereoscopic image and the secondstereoscopic image to a viewer.
 308. The method of claim 307, whereinthe at least one volumetric image comprises an attenuation value foreach of a first voxel and second voxel in the volumetric image, whereinthe attenuation value for the first voxel is indicative of an amount ofattenuation of an ultrasound signal passing through the first voxel.309. The method of claim 307, wherein the at least one volumetric imagecomprises a speed of sound value for each of a first voxel and a secondvoxel in the volumetric image, wherein the speed of sound value for thefirst voxel is indicative of a speed of an ultrasound signal passingthrough the first voxel.
 310. The method of claim 307, wherein saidaccessing comprises accessing multiple time-dependent volumetric imagesof the subject, wherein said applying comprises applying thestereoscopic conversion algorithm to the multiple volumetric images toobtain multiple stereoscopic images including the first stereoscopicimage and the second stereoscopic image, and wherein said displayingcomprises displaying, via the three-dimensional display, the multiplestereoscopic images to a viewer in a time-dependent manner.
 311. Themethod of claim 307, wherein the at least one volumetric image of thesubject comprises accessing a plurality of volumetric images of thesubject, wherein the method further comprises combining the plurality ofvolumetric images of the subject to form a fused volumetric image of thesubject, and wherein said applying comprises applying the stereoscopicconversion to the fused volumetric image to obtain the first and thesecond stereoscopic images.
 312. The method of claim 311, whereincombining the plurality of volumetric images comprises associating afirst visual cue to values in the fused image originating from a firstof the plurality of volumetric images and associating a second visualcue, different from the first visual cue, to values in the fused imageoriginating from a second of the plurality of images.
 313. The method ofclaim 307, further comprising: applying at least one image analysistechnique to the at least one volumetric image to identify at least oneshape in the at least one volumetric image; and updating the at leastone volumetric image, prior to applying the stereoscopic conversation tothe at least one volumetric image, so that the at least one volumetricimage shows the identified at least one shape when displayed.
 314. Themethod of claim 307, wherein the three-dimensional display is alenticular display.
 315. The method of claim 307, wherein saiddisplaying comprises presenting the first stereoscopic image and thesecond stereoscopic image with different polarizations.
 316. The methodof claim 307, further comprising: in response to said displaying,receiving input from the viewer specifying an update to how the at leastone volumetric image is displayed; and updating how the at least onevolumetric is displayed three dimensionally, via the three-dimensionaldisplay, based on the received input.
 317. A method, comprising:accessing at least one volumetric image of a subject calculated using aplurality of measurements of the subject, the plurality of measurementsresulting at least in part from the detection of radiation by an imagingdevice; identifying a point of view within the subject, whereinidentifying the point of view comprises identifying a location withinthe subject; and displaying the at least one volumetric image to aviewer from the identified point of view.
 318. The method of claim 317,wherein the imaging device is an ultrasound imaging device.
 319. Themethod of claim 318, wherein the plurality of measurements resulted atleast in part from the detection of ultrasound radiation by theultrasound imaging device operating in a transmissive modality.
 320. Themethod of claim 317, wherein said displaying comprises displayingthree-dimensionally, via a three-dimensional display, the at least onevolumetric image to the viewer from the identified point of view. 321.The method of claim 317, wherein said identifying comprises identifyinga plurality of points of view within the subject, including the point ofview, and wherein said displaying comprises displaying the at least onevolumetric image to the viewer from at least two of the identifiedpoints of view.
 322. The method of claim 321, wherein locationscorresponding to the plurality of points of view lie along a paththrough the subject, and wherein said displaying comprises displayingthe at least one volumetric image to the viewer in a sequencecorresponding to an ordering of the locations along the path.
 323. Themethod of claim 322, wherein said displaying comprises displaying, via athree-dimensional display, the at least one volumetric image from the atleast two of the identified points of view.
 324. The method of claim317, wherein said identifying further comprises identifying an anglewithin the subject.
 325. The method of claim 317, wherein saididentifying comprises identifying the point of view based at least inpart on input received from the viewer, wherein the input specifies thepoint of view.
 326. The method of claim 317, wherein said identifyingcomprises automatically identifying the point of view at least in partby applying an image analysis technique to the at least one volumetricimage.
 327. A method, comprising: displaying a volumetric image of asubject to a user three dimensionally via a three-dimensional display;obtaining user input identifying at least one target point in thevolumetric image corresponding to at least one location in the subject;and applying high intensity focused ultrasound (HIFU) energy to the atleast one location in the subject.
 328. The method of claim 327, whereinsaid obtaining comprises obtaining the user input at least in part bydetecting motion of the user and/or a pointing device of the userthrough the displayed volumetric image.
 329. The method of claim 327,wherein said obtaining comprises identifying a plurality of targetpoints in the volumetric image corresponding to a plurality of locationsalong a path through the subject.
 330. The method of claim 327, whereinsaid applying comprises applying the HIFU energy based at least in parton at least one HIFU parameter, the method further comprising:calculating the at least one HIFU control parameter.
 331. The method ofclaim 330, comprising performing said calculating based at least in parton user input specifying an amount of energy and/or power to apply tothe at least one location in the subject.
 332. The method of claim 330,wherein the at least one HIFU control parameter specifies how to focusthe HIFU energy to obtain a focused HIFU beam.
 333. The method of claim332, wherein performing said calculating comprises using a beamformingtechnique.
 334. The method of claim 332, wherein performing saidcalculating comprises using a time-reversal technique.
 335. The methodof claim 327, wherein the three-dimensional display is a lenticulardisplay.
 336. The method of claim 327, wherein said displaying comprisesapplying stereoscopic conversion to the volumetric image to obtain afirst stereoscopic image and a second stereoscopic image and displayingthree-dimensionally, via the three-dimensional display, the firststereoscopic image and the second stereoscopic image to the user.
 337. Amethod, comprising: applying high intensity focused ultrasound (HIFU)energy to a subject; identifying, based at least in part on an image ofthe subject, a first target point in the subject to which the HIFUenergy was applied; automatically determining whether to continueapplying the HIFU energy to the first target point at least in part bycomparing the first target point to a planned target point; andcontinuing to apply the HIFU energy to the first target point based atleast in part on the comparison.
 338. The method of claim 337, furthercomprising: applying the HIFU energy to the planned target point, basedat least in part on determining a difference between the first targetpoint and the planned target point as a result of the comparison. 339.The method of claim 337, wherein the image is a volumetric imageobtained by an imaging device.
 340. The method of claim 339, wherein theimaging device is an ultrasound imaging device operating in atransmissive modality.
 341. The method of claim 340, wherein theultrasound imaging device is further configured to perform saidapplying.
 342. The method of claim 337, wherein said identifying isperformed, automatically, by using a statistical inference technique.343. The method of claim 337, wherein said automatically determiningcomprises determining whether a difference between a position of thefirst target point and a position of the planned target point is below athreshold.
 344. A method, comprising: accessing a plurality ofmeasurements of a subject, the plurality of measurements resulting atleast in part from the detection of ultrasound radiation by anultrasound imaging device, the ultrasound imaging device comprising aplurality of ultrasound sources including a first ultrasound source anda plurality of ultrasound sensors including a first ultrasound sensor;calculating, using at least one processor, a first image of the subjectfrom the plurality of measurements by using first path lengthinformation for a path between the first ultrasound source and the firstultrasound sensor; calculating, using the at least one processor, secondpath length information at least in part by computing refractive pathsusing the first image; and calculating, using the at least oneprocessor, a second image of the subject from the plurality ofmeasurements by using the second path length information.
 345. Themethod of claim 344, wherein said calculating the second path lengthinformation comprises computing refractive paths using Fermat'sprinciple.
 346. The method of claim 345, wherein said calculating thesecond path length information further comprises obtaining a solution toa differential equation.
 347. The method of claim 344, wherein saidcalculating the first image of the subject comprises calculating thefirst image by using a compressive sensing image reconstructiontechnique.
 348. The method of claim 347, wherein said calculating thesecond image of the subject comprises calculating the second image byusing the compressive sensing image reconstruction technique.
 349. Themethod of claim 348, wherein using the compressive sensing imagereconstruction technique to calculate the first image of the subjectcomprises identifying a solution to a first system of linear equationsrelating the plurality of measurements to a property of the subject,wherein the first system of linear equations was obtained based at leastin part on first path length information.
 350. The method of claim 349,wherein using the compressive sensing image reconstruction technique tocalculate the second image of the subject comprises identifying asolution to a second system of linear equations relating the pluralityof measurements to the property of the subject, wherein the secondsystem of linear equations was obtained based at least in part on secondpath length information.
 351. The method of claim 344, wherein the firstimage of the subject is a volumetric image of the subject.
 352. Themethod of claim 344, wherein the second image of the subject is avolumetric image of the subject.
 353. The method of claim 344, whereinthe plurality of measurements was obtained by the ultrasound imagingdevice operating in a transmissive modality.
 354. An apparatus,comprising: a first ultrasound element configured as an ultrasoundsource; transmit circuitry coupled to the ultrasound source andconfigured to provide to the ultrasound source a transmission signal tobe emitted by the ultrasound source; a second ultrasound elementconfigured as an ultrasound sensor; processing circuitry coupled to theultrasound sensor and configured to process a signal emitted by theultrasound source and received by the ultrasound sensor, wherein theprocessing circuitry is configured to combine the signal received by theultrasound sensor with a reference signal to produce a combined signal.355. The apparatus of claim 354, wherein the reference signal is thetransmission signal.
 356. The apparatus of claim 354, wherein thereference signal is a chirp.
 357. The apparatus of claim 354, whereinthe processing circuitry is configured to generate the reference signal.358. The apparatus of claim 357, wherein the processing circuitry isconfigured to generate the reference signal at least in part by using alocal oscillator.
 359. The apparatus of claim 354, wherein theprocessing circuitry is configured to combine the signal received by theultrasound sensor with the reference signal by multiplying the receivedsignal with the reference signal to obtain the combined signal.
 360. Theapparatus of claim 354, wherein the processing circuitry comprises amixer having a first input configured to receive the signal received bythe ultrasound sensor and a second input configured to receive thetransmission signal from the transmit circuitry.
 361. The apparatus ofclaim 354, wherein the processing circuitry comprises a low pass filterconfigured to be applied to the combined signal.
 362. The apparatus ofclaim 354, wherein the processing circuitry is configured to perform aFourier transform on the combined signal.
 363. The apparatus of claim354, wherein the processing circuitry is configured to combine thereceived signal with the reference signal before the received signal isprocessed by an analog-to-digital converter.
 364. An apparatus,comprising: a support; a first plurality of ultrasound elementsconfigured as ultrasound imaging elements; and a second plurality ofultrasound elements configured as high intensity focused ultrasound(HIFU) elements, wherein the first plurality and second plurality ofultrasound elements are physically coupled to the first support, andwherein at least some elements of the first plurality of ultrasoundelements are arranged among at least some elements of the secondplurality of ultrasound elements.
 365. The apparatus of claim 364,wherein each of the first plurality of ultrasound imaging elements isconfigured to perform at least one of emission of a radiation sourcesignal incident upon a volume to be imaged three-dimensionally ordetection of such a radiation source signal.
 366. The apparatus of claim365, wherein the second plurality of ultrasound elements is configuredto emit ultrasound radiation of sufficient intensity to induce a changein a tissue state of tissue located within the volume.
 367. Theapparatus of claim 364, wherein at least some elements of the firstplurality of ultrasound elements are interspersed with at least someelements of the second plurality of ultrasound elements.
 368. Theapparatus of claim 364, wherein at least some elements of the firstplurality of ultrasound elements are interleaved with at least someelements of the second plurality of ultrasound elements.
 369. Theapparatus of claim 364, wherein the first plurality of ultrasoundelements and the second plurality of ultrasound elements are arranged incombination in a checkerboard pattern.
 370. The apparatus of claim 364,wherein the second plurality of ultrasound elements are configured tocollectively define a HIFU focal length movable in three dimensions.371. The apparatus of claim 364, wherein at least one ultrasound elementof the first plurality of ultrasound elements is configured to exhibittime-varying operation as an ultrasound imaging element and as a HIFUelement.
 372. The apparatus of claim 364, wherein at least oneultrasound element of the second plurality of ultrasound elements isconfigured to exhibit time-varying operation as a HIFU element and as anultrasound imaging element.
 373. The apparatus of claim 364, wherein thefirst plurality of ultrasound elements and/or the second plurality ofultrasound elements is arranged in at least two dimensions.
 374. Theapparatus of claim 373, wherein both the first plurality of ultrasoundelements and second plurality of ultrasound elements are arranged in atleast two dimensions.
 375. The apparatus of claim 373, wherein the firstplurality of ultrasound elements is arranged in at least two dimensions.376. The apparatus of claim 375, wherein the first plurality ofultrasound elements is arranged in three dimensions.
 377. The apparatusof claim 375, wherein the first plurality of ultrasound elements isarranged in an array of at least two dimensions in which the firstplurality of ultrasound elements adopts a regular spacing.
 378. Theapparatus of claim 373, wherein the second plurality of ultrasoundelements is arranged in at least two dimensions.
 379. The apparatus ofclaim 378, wherein the second plurality of ultrasound elements isarranged in three dimensions.
 380. The apparatus of claim 378, whereinthe second plurality of ultrasound elements is arranged in an array ofat least two dimensions.
 381. The apparatus of claim 364, wherein thefirst plurality of ultrasound elements is configured to emit and/orreceive ultrasound signals of wavelength λ, and wherein a minimumspacing between nearest neighbor ultrasound elements of the firstplurality of ultrasound imaging elements is greater than λ/2.
 382. Theapparatus of claim 364, wherein the support is a first support, andwherein the apparatus further comprises: a second support; a thirdplurality of ultrasound elements configured as ultrasound imagingelements; and a fourth plurality of ultrasound elements configured asHIFU elements, wherein the third plurality and fourth plurality ofultrasound elements are physically coupled to the second support andwherein the third plurality and fourth plurality of ultrasound elementsare in a substantially fixed relationship with respect to each other,and wherein at least some elements of the third plurality of ultrasoundelements are arranged among at least some elements of the fourthplurality of ultrasound elements.
 383. The apparatus of claim 382,wherein the second support is a flexible support.
 384. The apparatus ofclaim 382, wherein the first and second supports are moveable relativeto each other, to change position and/or orientation of the firstplurality of ultrasound elements relative to the third plurality ofultrasound imaging elements.
 385. The apparatus of claim 384, furthercomprising at least one detector configured to detect position and/ororientation of the first plurality of ultrasound elements relative tothe third plurality of ultrasound elements.
 386. The apparatus of claim385, wherein the at least one detector is configured to dynamicallydetect position and/or orientation during operation of the firstplurality of ultrasound elements and/or the third plurality ofultrasound elements.
 387. The apparatus of claim 385, wherein the atleast one detector is physically coupled to the first support.
 388. Theapparatus of claim 384, further comprising circuitry configured toreceive signals from the first plurality and/or third plurality ofultrasound elements and process the signals to determine position and/ororientation of the first plurality of ultrasound elements relative tothe third plurality of ultrasound elements.
 389. The apparatus of claim364, wherein the first plurality and second plurality of ultrasoundelements are in a substantially fixed relationship with respect to eachother.
 390. The apparatus of claim 364, wherein the support is aflexible support.
 391. A system, comprising: a first support; a secondsupport; a first plurality of ultrasound elements configured as highintensity focused ultrasound (HIFU) elements and physically coupled tothe first support and configured as a first source of HIFU; a secondplurality of ultrasound elements configured as ultrasound imagingelements and coupled to the first support and distinct from the firstplurality of ultrasound elements; a third plurality of ultrasoundelements configured as HIFU elements and physically coupled to thesecond support and configured as a second source of HIFU; and a fourthplurality of ultrasound elements configured as ultrasound imagingelements and coupled to the second support and distinct from the thirdplurality of ultrasound elements; wherein the second plurality ofultrasound elements and the fourth plurality of ultrasound elements areconfigured to operate in combination in a transmissive ultrasoundimaging modality.
 392. The apparatus of claim 391, wherein the firstsupport and second support are independently movable.
 393. The apparatusof claim 391, further comprising control circuitry coupled to the first,second, third, and fourth pluralities of ultrasound elements andconfigured to control application of HIFU by the first and thirdpluralities of ultrasound elements and to control imaging operation ofthe second and fourth pluralities of ultrasound elements.
 394. Theapparatus of claim 391, further comprising a detector configured todetect relative position and/or orientation of the second plurality ofultrasound elements relative to the fourth plurality of ultrasoundelements.
 395. The apparatus of claim 391, wherein the second and fourthpluralities of ultrasound elements each include at least twenty-fiveultrasound elements.
 396. An apparatus, comprising; a substrate; a firstplurality of ultrasound elements configured as ultrasound imagingelements coupled to the substrate; and a second plurality of ultrasoundelements configured as high intensity focused ultrasound (HIFU) elementscoupled to the substrate.
 397. The apparatus of claim 396, wherein thesubstrate is formed of an acoustically insulating material.
 398. Theapparatus of claim 396, wherein at least some elements of the firstplurality of ultrasound elements are arranged among at least someelements of the second plurality of ultrasound elements.
 399. Theapparatus of claim 396, wherein at least some elements of the firstplurality of ultrasound elements are interspersed with at least someelements of the second plurality of ultrasound elements.
 400. Theapparatus of claim 396, wherein at least some elements of the firstplurality of ultrasound elements are interleaved with at least someelements of the second plurality of ultrasound elements.
 401. Theapparatus of claim 396, wherein the first plurality of ultrasoundelements and the second plurality of ultrasound elements are arranged incombination in a checkerboard pattern.
 402. The apparatus of claim 396,wherein each of the first plurality of ultrasound imaging elements isconfigured to perform at least one of emission of a radiation sourcesignal incident upon a volume to be imaged three-dimensionally ordetection of such a radiation source signal.
 403. The apparatus of claim402, wherein the second plurality of ultrasound elements is configuredto emit ultrasound radiation of sufficient intensity to induce a changein a tissue state of tissue located within the volume.
 404. Theapparatus of claim 396, wherein the first plurality of ultrasoundelements is configured to emit and/or receive ultrasound signals ofwavelength λ, and wherein a minimum spacing between nearest neighborultrasound elements of the first plurality of ultrasound imagingelements is greater than λ/2.
 405. The apparatus of claim 396, whereinthe first plurality of ultrasound elements is disposed on the substrate,and wherein the second plurality of ultrasound elements is disposed onthe substrate.